Etching method, semiconductor and fabricating method for the same

ABSTRACT

An organic/inorganic hybrid film represented by SiC x− H y O z  (x&gt;0, y≧0, z&gt;0) is plasma-etched with an etching gas containing fluorine, carbon and nitrogen. During the etching, a carbon component is eliminated from the surface portion of the organic/inorganic hybrid film due to the existence of the nitrogen in the etching gas, to thereby reform the surface portion. The reformed surface portion is nicely plasma-etched with the etching gas containing fluorine and carbon.

This application is a division of U.S. application Ser. No. 09/837,556filed on Apr. 19, 2001, now U.S. Pat. No. 6,632,746.

BACKGROUND OF THE INVENTION

The present invention relates to a method for etching anorganic/inorganic hybrid film represented by SiC_(x)H_(y)O_(z) (x>0,y≧0, z>0), a semiconductor device having an interlayer insulating filmmade of the organic/inorganic hybrid film, and a fabricating method forsuch a semiconductor device.

Recent semiconductor integrated circuit devices adopt multilayerinterconnection structures to meet requests for size scale-down andhigher integration. Conventionally, a silicon oxide (SiO₂) film has beenused as an interlayer insulating film provided between lowerinterconnections and upper interconnections. Contact holes are formedthrough such an interlayer insulating film by plasma etching forconnection with lower interconnections when a multilayer interconnectionstructure is adopted.

Hereinafter, as a first conventional example, an etching method forformation of contact holes through an interlayer insulating film made ofa silicon oxide film will be described with reference to FIGS. 22( a) to22(d).

First, as shown in FIG. 22( a), a lower interconnection 12 made ofcopper, for example, is formed in an insulating film 11 deposited on asemiconductor substrate 10 by a known method. On the lowerinterconnection 12, deposited is an etching stopper film 13 made of asilicon nitride (Si₃N₄) film, for example, that has the function ofpreventing the lower interconnection 12 from oxidizing during etchingand also stopping the etching. An interlayer insulating film 14 made ofa silicon oxide (SiO₂) film is deposited on the etching stopper film 13.A resist pattern 15 having an opening for formation of a contact hole isthen formed on the interlayer insulating film 14. Note that, althoughillustration is omitted, the sides and the bottom of the lowerinterconnection 12 are normally coated with barrier metal.

Thereafter, as shown in FIG. 22( b), a contact hole 16 is formed throughthe interlayer insulating film 14 using the resist pattern 15 as a maskby plasma etching with an etching gas containing fluorine and carbon,such as CF₄ gas, C₂F₆ gas, C₃F₈ gas, CHF₃ gas, C₃F₈ gas, or C₄F₈ gas.

As shown in FIG. 22( c), the resist pattern 15 is removed by ashing withoxygen plasma. As shown in FIG. 22( d), the portion of the etchingstopper layer 13 exposed in the contact hole 16 is removed.

In recent years, further scale-down and higher integration of multilayerinterconnection structures have been demanded, and with realization ofthis demand, signal delay at interconnections has become greatlyinfluential to the operation speed of a semiconductor integratedcircuit.

In order to reduce signal delay at interconnections, it has beenproposed to use a film having a low dielectric constant (ε=2 to 3) asthe interlayer insulating film. As such a film having a low dielectricconstant, known are an organic insulating film containing an organiccompound as a main component, a fluorine-containing insulating film madeof a fluorine-containing silicon oxide (SiOF), and an organic/inorganichybrid film represented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z>0). JapaneseLaid-Open Patent Publication No. 10-125674 proposes an organic/inorganichybrid film made of a silicon oxide film containing carbon and hydrogen,deposited by feeding hexamethyldisiloxane (HMDSO) as a material gas.

The organic insulating film, of which the composition is similar to thatof a resist film, has the following problem. When a resist patternformed on the organic insulating film is to be removed by ashing withoxygen plasma, the organic insulating film itself is damaged by theoxygen plasma. The fluorine-containing insulating film has the problemthat it easily comes off due to its poor adhesion to an underlying filmand also it is poor in mechanical strength and heat resistance.

The organic/inorganic hybrid film has a specific dielectric constantconsiderably smaller than the fluorine-containing insulating film andhas a mechanical strength roughly equal to that of thefluorine-containing insulating film. Moreover, the organic/inorganichybrid film, of which the composition is not similar to that of a resistfilm, is less damaged by oxygen plasma, and therefore, the resistpattern can be removed by ashing with oxygen plasma.

In consideration of the above, the organic/inorganic hybrid film ispromising as an interlayer insulating film having a low specificdielectric constant.

With the recent demand for size scale-down and higher integration ofsemiconductor integrated circuit devices, also, the diameter of contactholes formed through the interlayer insulating film has become finer andthe aspect ratio of the contact holes has become larger. It is difficultto fill such fine contact holes having a large aspect ratio with aconductive material with reliability.

To solve the above problem, Japanese Laid-Open Patent Publication No.8-191062, for example, proposes a technique in which the diameter of thecontact holes is made larger near the opening thereof than near thebottom thereof, to facilitate filling of the contact holes with aconductive material.

Hereinafter, as the second conventional example, the etching methoddisclosed in Japanese Laid-Open Patent Publication No. 8-191062 will bedescribed with reference to FIGS. 23( a) to 23(d). Note that in FIGS.23( a) to 23(d), illustration of a lower interconnection is omitted.

First, as shown in FIG. 23( a), a resist pattern 15 having an opening 15a for formation of a contact hole is formed on an interlayer insulatingfilm 14 made of a silicon oxide film deposited on a semiconductorsubstrate 10.

As shown in FIG. 23( b), the interlayer insulating film 14 is subjectedto anisotropic dry etching with an etching gas containing fluorine andcarbon using the resist pattern 15 as a mask, to form a contact hole 16to reach partway in the interlayer insulating film 14.

Isotropic dry etching is then performed for the interlayer insulatingfilm 14 with an etching gas including oxygen gas. By this etching, asshown in FIG. 23( c), an opening 15 a of the resist pattern 15 iswidened, and with this, the diameter of the contact hole 16 is madelarger near the opening thereof, to provide a tapered wall at theopening of the contact hole 16.

As shown in FIG. 23( d), the resist pattern 15 is removed. Althoughillustration is omitted, by depositing a conductive material on theinterlayer insulating film 14, the contact hole 16 is filled with theconductive material with reliability.

(First Problem)

The plasma etching for forming fine contact holes through anorganic/inorganic hybrid film is normally performed with an etching gascontaining fluorine and carbon, which can cleave Si—O bonds, as in theplasma etching of a silicon oxide film.

However, when the organic/inorganic hybrid film is etched with the sameetching gas under the same conditions as those used for etching of thesilicon oxide film, the etching rate largely decreases, or in an extremecase, the etching itself stops. The decrease in etching rate causesreduction in throughput. This also causes reduction in the differencebetween the etching rate of the interlayer insulating film and that ofthe resist pattern, failing to secure a sufficiently large etchingselection ratio.

By adding oxygen gas to the etching gas, the etching rate of theorganic/inorganic hybrid film increases. However, this also facilitatesetching of the resist pattern 15, and thus the etching selection ratioof the interlayer insulating film 14 to the resist pattern 15 decreases.

The addition of oxygen gas to the etching gas also increases the etchingrate of the silicon nitride film constituting the etching stopper film13. This reduces the etching selection ratio of the interlayerinsulating film 14 to the etching stopper film 13.

Therefore, it is not preferable to add oxygen gas to the etching gas.

In view of the above, the first object of the present invention isproviding good plasma etching for an organic/inorganic hybrid film.

(Second Problem)

As described above, the etching stopper film 13 made of silicon nitridefilm is deposited on the lower interconnection 12 made of a copper film,for example. The specific dielectric constant of the silicon nitridefilm is about 7, which is significantly large compared with the specificdielectric constant of the organic/inorganic hybrid film.

Having such an etching stopper film, therefore, the reduction inspecific dielectric constant between the upper and lowerinterconnections is not sufficiently attained despite of the formationof the interlayer insulating film 14 made of the organic/inorganichybrid film in an attempt to reduce the specific dielectric constant.

In view of the above, the second object of the present invention isreducing the specific dielectric constant between the upper and lowerinterconnections by reducing the specific dielectric constant of theetching stopper film.

(Third Problem)

The second conventional example described above is an etching techniquein which the resist film is etched more isotropically to widen theopenings of the resist film by adding oxygen gas to the etching gas, tothereby provide contact holes having a tapered opening. However, thistechnique requires a large amount of etching of the resist film, andtherefore it is not possible to increase the thickness of the resistfilm in an attempt to form contact holes having a large aspect ratio.For this reason, the second conventional example finds difficulty inapplication to formation of contact holes having a large aspect ratio.In particular, in the case of forming tapered contact holes through theinterlayer insulating film made of an organic/inorganic hybrid film, howthe etching amount of the resist film should be reduced is a big problemto be solved.

There is also reported a technique in which the contact holes are etchedinto a tapered shape using an etching gas containing fluorine and carbonwithout changing the diameter of the openings of the resist film.However, whether or not this technique is applicable to the formation ofcontact holes through the interlayer insulating film made of anorganic/inorganic hybrid film has not been verified.

In view of the above, the third object of the present invention isproviding a method in which contact holes having an increased diameternear the opening thereof can be formed through an interlayer insulatingfilm made of an organic/inorganic hybrid film with reliability.

(Fourth Problem)

In recent years, in order to enhance the resolution between lightexposed portions and non-exposed portions of a resist film, there hasbeen proposed a technique of forming a resist pattern using a chemicalamplification resist material. According to this technique, the polarity(solubility to a developer) is changed in portions of the resist filmmade of a chemical amplification resist material exposed to an energybeam by the function of acid generated in the exposed portions. Theexposed portions or non-exposed portions are then removed with thedeveloper, to form a resist pattern.

The present inventors formed a resist film by applying a chemicalamplification resist material to an organic/inorganic hybrid film, andsubjected the resist film to pattern light exposure. As a result, it wasfound that exposed portions of the resist film failed to sufficientlychange the polarity presumably due to a reduced amount of acid generatedin the exposed portions. Therefore, the resultant resist pattern afterremoval of the exposed portions or non-exposed portions of the resistfilm with a developer was faulty in shape.

The present inventors attempted to increase the exposure amount duringthe pattern light exposure, but failed to sufficiently change thepolarity of the exposed portions of the resist film.

The faulty formation of the resist pattern did not occur when a chemicalamplification resist film was formed on a silicon oxide film, but wasunique to the chemical amplification resist film formed on anorganic/inorganic hybrid film. The faulty formation of the resistpattern was confirmed to occur when using a positive chemicalamplification resist film, but is presumed to also occur when using anegative chemical amplification resist film.

Hereinafter, a problem occurring in the formation of multilayerinterconnections having a dual damascene structure, which uses achemical amplification resist pattern formed on an organic/inorganichybrid film, will be described with reference to FIGS. 24( a), 24(b),and 25.

First, as shown in FIG. 24( a), a lower interconnection 22 is formed onan insulating film 21 deposited on a semiconductor substrate 20. Anetching stopper film 23 is deposited on the lower interconnection 22,and then an interlayer insulating film 24 made of an organic/inorganichybrid film is deposited on the etching stopper film 23. Thereafter, acontact hole 25 is formed through the interlayer insulating film 24 byplasma etching using a first resist pattern that is formed on theinterlayer insulating film 24 and has an opening for formation of thecontact hole.

A chemical amplification resist material is then applied to theresultant interlayer insulating film 24 to form a resist film. Theresist film is then subjected to pattern light exposure and development,to form a second resist pattern 26 having an opening for formation of aninterconnection groove. At this stage, the resist film partly remainsafter the above processing, forming a resist film 26 a over the topsurface of the interlayer insulating film 24 as well as the wall and thebottom of the contact hole 25. The reason why the resist film 26 a isformed is considered that acid has been reacted with some reactive groupand consumed.

Thereafter, the interlayer insulating film 24 is subjected to plasmaetching using the second resist pattern 26 as a mask, to form aninterconnection groove 27 in the interlayer insulating film 24 as shownin FIG. 24( b). During this etching, a barrier (inner crown) 28 made ofthe interlayer insulating film 24 is formed since the resist film 26 aon the inner side of the interconnection groove 27 serves as a mask.

After removal of the second resist pattern 26 and the resist film 26 aas shown in FIG. 25, the contact hole 0.25 and the interconnectiongroove 27 are filled with a conductive material to form a plug and anupper interconnection. At this time, due to the existence of the barrier28 on the inner side of the interconnection groove 27, the contactresistance between the upper interconnection embedded in theinterconnection groove 27 and the plug embedded in the contact hole 25disadvantageously increases.

In view of the above, the fourth object of the present invention ispreventing deactivation of acid in a chemical amplification resist filmformed on an organic/inorganic hybrid film, to improve the resolution ofthe resist film.

SUMMARY OF THE INVENTION

(First Resolution Principle)

In order to solve the first problem, the present inventors examined thereason for the reduction of the etching rate when an organic/inorganichybrid film is subjected to plasma etching with an etching gascontaining fluorine and carbon, and found the following.

FIG. 26( a) illustrates a cross-sectional structure of a contact hole 16formed by dry-etching an interlayer insulating film 14A made of asilicon oxide film with an etching gas containing fluorine and carbon.FIG. 26( b) illustrates a cross-sectional structure of a contact hole 16formed by dry-etching an interlayer insulating film 14B made of anorganic/inorganic hybrid film with an etching gas containing fluorineand carbon.

An etching gas normally contains a carbon component for protection ofthe resist pattern 15. Therefore, in the dry etching of the interlayerinsulating film 14A made of a silicon oxide film, a thin polymer film17A is deposited on a wall 16 a and a bottom 16 b of the contact hole 16as shown in FIG. 26( a). In this process, therefore, both the depositionof the polymer film 17A and the etching proceed competing with eachother at the wall 16 a and the bottom 16 b of the contact hole 16. Atthe bottom 16 b, however, the etching predominates over the deposition.Accordingly, the bottom 16 b of the contact hole 16 moves downward, thatis, toward the etching stopper film 13.

In the case of dry etching of the interlayer insulating film 14B made ofan organic/inorganic hybrid film, a carbon component is contained, notonly in the etching gas, but also in the organic/inorganic hybrid film.Therefore, as shown in FIG. 26( b), an etching reaction gas containing acarbon component is generated at the wall 16 a and the bottom 16 b ofthe contact hole 16 during the etching of the organic/inorganic hybridfilm. As a result, a polymer film 17B having a larger thickness thanthat shown in FIG. 26( a) is deposited. In this case, also, both thedeposition of the polymer film 17B and the etching proceed competingwith each other at the bottom 16 b of the contact hole 16. However, inthis case, progress of the etching is blocked by the carbon component atthe bottom 16 b as the etching surface of the organic/inorganic hybridfilm, together with the polymer film 17B. In the early stage of theetching, that is, when the depth of the contact hole 16 is small, whenthe introduced amount of the plasma etching species and the plasmaenergy are sufficient, the etching predominates over the deposition ofthe polymer film 17B, and therefore the etching proceeds. As the contacthole 16 becomes deeper with the progress of the etching, however, theintroduced amount of the plasma etching species and the plasma energybecome insufficient, failing to sufficiently remove the carbon componentin the organic/inorganic hybrid film. Therefore, a surplus of the carboncomponent is accumulated on the bottom 16 b of the contact hole 16,blocking smooth etching reaction. Since the deposition of the polymerfilm 17B predominates over the etching, the etching rate graduallydecreases, and finally the etching stops.

In consideration of the above, if the etching is carried out whilesufficiently removing the polymer film on the bottom of the contact holeand the carbon component existing in the portion of theorganic/inorganic hybrid film exposed in the contact hole, the etchingshould proceed smoothly.

The first and second etching methods according to the present inventionare based on the first resolution principle described above.

The first etching method of the present invention is directed to amethod for plasma-etching an organic/inorganic hybrid film representedby SiC_(x)H_(y)O_(z) (x>0, y≧0, z>0), including the step of:plasma-etching the organic/inorganic hybrid film while eliminating acarbon component from a surface portion of the organic/inorganic hybridfilm.

According to the first etching method, the plasma etching is performedwhile the surface portion of the organic/inorganic hybrid film isreformed by elimination of a carbon component from the surface portionof the organic/inorganic hybrid film. Therefore, in thecarbon-eliminated surface portion, in which the amount of the carboncomponent that facilitates deposition of a polymer film is small, theetching rate improves.

The second etching method of the present invention is directed to amethod for plasma-etching an organic/inorganic hybrid film representedby SiC_(x)H_(y)O_(z) (x>0, y≧0, z>0), including repeating alternately afirst step of eliminating a carbon component from a surface portion ofthe organic/inorganic hybrid film and a second step of plasma-etchingthe surface portion from which the carbon component has been eliminated.

According to the second etching method, the first step of eliminating acarbon component from the surface portion of the organic/inorganichybrid film and the second step of plasma-etching the surface portionfrom which the carbon component has been eliminated are performedalternately. Therefore, in the carbon-eliminated surface portion, inwhich the amount of the carbon component that facilitates deposition ofa polymer film is small, the etching rate improves.

In the first or second etching method, plasma etching is performed inthe state where the carbon component has been eliminated from thesurface portion of the organic/inorganic hybrid film, that is, in thestate where the amount of the carbon component that blocks cleaving ofSi—O bonds and generation of CO₂, SiF₄, and the like is small in thesurface portion of the organic/inorganic hybrid film. Therefore, theetching rate improves. This improves the throughput and also increasesthe etching selection ratio with respect to the resist pattern.

The second etching method is especially effective in the case that thepreferred conditions under which the carbon component is eliminated fromthe surface portion are different from the preferred conditions underwhich the surface portion is plasma-etched, such as the case that thepreferred gas pressure adopted when the carbon component is eliminatedfrom the surface portion is largely different from the preferred gaspressure adopted when the organic/inorganic hybrid film isplasma-etched.

In the first etching method, the plasma etching is preferably performedwith an etching gas containing fluorine, carbon and nitrogen.

In the second etching method, preferably, the first step is performedwith a gas containing nitrogen, and the second step is performed with anetching gas containing fluorine and carbon.

In the above case, the gas containing nitrogen may be a mixed gas ofhydrogen and nitrogen or ammonia gas.

When a gas containing nitrogen comes into contact with the surface of anorganic/inorganic hybrid film represented by SiC_(x)H_(y)O_(z) (x>0,y≧0, z>0), “C_(x)H_(y)” is chemically changed to highly volatile HCN orCN at the surface of the SiC_(x)H_(y)O_(z) film, and thus the proportionof the carbon component decreases in the surface portion of theorganic/inorganic hybrid film (SiC_(x)H_(y)O₂ film). Therefore, theetching of the organic/inorganic hybrid film proceeds at roughly thesame etching rate as that for a silicon oxide film. This mechanism willbe described according to reaction formulae as follows.

When a gas containing nitrogen comes into contact with the surface ofthe organic/inorganic hybrid film represented by SiC_(x)H_(y)O_(z),chemical reaction represented by Formula 1 or Formula 2 below proceeds.

That is, in the surface portion of the organic/inorganic hybrid film,the carbon component is eliminated, to provide a reformed film having acomposition similar to that of a silicon oxide film.

Thereafter, when an etching gas containing fluorine and carbon comesinto contact with the reformed layer of the organic/inorganic hybridfilm, the CF_(x) contained in the etching gas reacts with the reformedlayer as represented by Formula 3 or Formula 4 below, and thus etchingproceeds.

Thus, “C_(x)H_(y)” is removed from the surface portion of theSiC_(x)H_(y)O_(z) film, to form the reformed layer represented bySiH_(y−x)O_(z) or SiH_(y)O_(z), and the reformed layer is then etchedwith an etching gas containing fluorine and carbon. In this way, theplasma etching can be performed for the organic/inorganic hybrid film(SiC_(x)H_(y)O_(z) film) at roughly the same etching rate as that for asilicon oxide film (SiO₂ film).

The above phenomenon that C or C_(x)H_(y) is removed from theSiC_(x)H_(y)O_(z) film implies that the proportion of oxygen atoms inthe film increases. This phenomenon can therefore be considered asoxidation.

The reformation of the surface portion of the SiC_(x)H_(y)O_(z) film isa process of removing the carbon component in the surface portion of theSiC_(x)H_(y)O_(z) film by changing the carbon component to HCN or CN.Therefore, if no hydrogen atoms or only a small amount of hydrogen atomsare contained in the SiC_(x)H_(y)O_(z) film, hydrogen gas may be mixedin the gas for reformation to enable efficient progress of thereformation and thus the etching.

In plasma etching of an inorganic insulating film containing no carboncomponent at all, such as a SiOF film, there is known an etching methodusing an etching gas obtained by mixing a nitride such as NH₃ in a CF₄gas that is normally used for etching of a silicon oxide film (JapaneseLaid-Open Patent Publication No. 9-263050).

The above conventional etching method is based on a technical thought asfollows. By mixing a nitride in the etching gas, fluorine radicals (F*)in the plasma of the etching gas are scavenged by hydrogen atoms (H),nitrogen atoms (N), or active species thereof freely existing in theplasma, to thereby enhance the selectivity with respect to a siliconsubstrate or a resist film. This technical thought in Japanese Laid-OpenPatent Publication No. 9-263050 is therefore completely different fromthe etching method of the present invention in which a gas containing anitrogen component is used for eliminating a carbon component from thesurface portion of an organic/inorganic hybrid film represented bySiC_(x)H_(y)O_(z).

(Second Resolution Principle)

The second resolution principle is for solving the second problemdescribed above. This utilizes the mechanism that the etching rate isreduced by the existence of a carbon component contained in anorganic/inorganic hybrid film represented by SiC_(x)H_(y)O_(z). That is,an organic/inorganic hybrid film is used as the etching stopper film, inplace of a silicon nitride film conventionally used. More specifically,under the interlayer insulating film made of an organic/inorganic hybridfilm, an etching stopper film made of an organic/inorganic hybrid filmin which the proportion of the carbon component is large compared withthe interlayer insulating film is provided.

In place of the organic/inorganic hybrid film, any of silicon insulatingfilms in which the proportion of the carbon component is large, such asa SiC film and the like, may be used.

The first fabricating method for a semiconductor device of the presentinvention includes the steps of: depositing an etching stopper film onan interconnection layer formed on a substrate, the etching stopper filmbeing represented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z≧0) in which theproportion of carbon atoms with respect to silicon atoms is relativelylarge; depositing an interlayer insulating film on the etching stopperfilm, the interlayer insulating film being represented bySiC_(x)H_(y)O_(z) (x>0, y≧0, z>0) in which the proportion of carbonatoms with respect to silicon atoms is relatively small; and forming acontact hole through the interlayer insulating film by plasma-etchingthe interlayer insulating film.

The first semiconductor device of the present invention includes: anetching stopper film formed on an interconnection layer formed on asubstrate, the etching stopper film being represented bySiC_(x)H_(y)O_(z) (x>0, y≧0, z≧0) in which the proportion of carbonatoms with respect to silicon atoms is relatively large; an interlayerinsulating film formed on the etching stopper film, the interlayerinsulating film being represented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z>0)in which the proportion of carbon atoms with respect to silicon atoms isrelatively small; and a contact hole formed through the interlayerinsulating film by plasma etching.

According to the first fabricating method of a semiconductor device andthe first semiconductor device, the etching stopper film containing acarbon component in a large proportion compared with the interlayerinsulating film is formed under the interlayer insulating film.Therefore, once the plasma etching of the interlayer insulating film iscompleted, the following phenomenon occurs. The etching stopper filmcontaining a larger amount of a carbon component is more or less etchedand generates an etching reaction gas containing a carbon component,which is mixed in the plasma. In addition, a large amount of the carboncomponent exists in the etching stopper film and on the surface thereof.Therefore, a thick polymer film is deposited on the bottom of thecontact hole, and this sharply reduces the etching rate of the etchingstopper film.

Thus, the etching stopper film made of the second organic/inorganichybrid film in which the proportion of the carbon component isrelatively large serves as the etching stopper film for the interlayerinsulating film made of the first organic/inorganic hybrid film in whichthe proportion of the carbon component is relatively small when thelatter is plasma-etched to form a contact hole.

In addition, since the above etching stopper film is made of aninsulating film having a low specific dielectric constant, the specificdielectric constant between the lower and upper interconnections can belargely reduced, compared with the case of using a silicon nitride filmhaving a large specific dielectric constant.

In the first fabricating method of a semiconductor device, the plasmaetching is performed with an etching gas containing fluorine, carbon andnitrogen.

(Third Resolution Principle)

The third resolution principle is for solving the third problemdescribed above. This utilizes the mechanism that the etching rate isreduced by the existence of a carbon component contained in anorganic/inorganic hybrid film represented by SiC_(x)H_(y)O_(z).Specifically, the mechanism is that with increase in the amount of thecarbon component contained in an organic/inorganic hybrid film, thepolymer film deposited on the wall of a contact hole is thicker and thisreduces the etching rate, and with decrease in the amount of the carboncomponent contained in the organic/inorganic hybrid film, the polymerfilm deposited on the wall of the contact hole is thinner and thisincreases the etching rate. The third resolution principle can berealized by the following first and second schemes.

In the first scheme, the lower part of the interlayer insulating film ismade of a first organic/inorganic hybrid film that contains a carboncomponent in a relatively small proportion, and the upper part of theinterlayer insulating film is made of a second organic/inorganic hybridfilm that contains a carbon component in a relatively large proportion.Plasma etching is carried out for the upper and lower parts of theinterlayer insulating film under the same conditions.

In the second scheme, a fixed proportion of a carbon component iscontained in the interlayer insulating film made of an organic/inorganichybrid film. In the early stage of plasma etching of the interlayerinsulating film (etching of the upper part of the interlayer insulatingfilm), the amount of the carbon component eliminated from the wall andthe bottom of the contact hole is kept relatively small, while in thelate stage of the plasma etching of the interlayer insulating film(etching of the lower part of the interlayer insulating film), theamount of the carbon component eliminated from the wall and the bottomof the contact hole is made relatively large.

The second fabricating method for a semiconductor device of the presentinvention, which embodies the first scheme of the third resolutionprinciple, includes the steps of: depositing a first interlayerinsulating film on an interconnection layer formed on a substrate, thefirst interlayer insulating film being represented by SiC_(x)H_(y)O_(z)(x>0, y≧0, z≧0) in which the proportion of carbon atoms with respect tosilicon atoms is relatively small; depositing a second interlayerinsulating film on the first interlayer insulating film, the secondinterlayer insulating film being represented by SiC_(x)H_(y)O_(z) (x>0,y≧0, z>0) in which the proportion of carbon atoms with respect tosilicon atoms is relatively large; and plasma-etching the secondinterlayer insulating film and the first interlayer insulating filmsequentially, to form a first opening through the second interlayerinsulating film, the diameter of the first opening being smaller towardthe bottom end, and a second opening through the first interlayerinsulating film, the wall of the second opening being vertical to thebottom surface.

The second semiconductor device of the present invention includes: afirst interlayer insulating film deposited on a substrate, the firstinterlayer insulating film being represented by SiC_(x)H_(y)O_(z) (x>0,y≧0, z≧0) in which the proportion of carbon atoms with respect tosilicon atoms is relatively small; a second interlayer insulating filmdeposited on the first interlayer insulating film, the second interlayerinsulating film being represented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z>0)in which the proportion of carbon atoms with respect to silicon atoms isrelatively large; a first opening formed through the second interlayerinsulating film by plasma-etching, the diameter of the first openingbeing smaller toward the bottom end; and a second opening formed underthe first opening through the first interlayer insulating film, the wallof the second opening being vertical to the bottom surface.

According to the second fabricating method for a semiconductor deviceand the second semiconductor device, the second interlayer insulatingfilm deposited on the first interlayer insulating film contains a largerproportion of the carbon component than the first interlayer insulatingfilm. Therefore, the following phenomenon occurs during the plasmaetching of the second interlayer insulating film. Both the deposition ofa polymer film and the etching proceeds competing with each other at thebottom of the first opening. In this occasion, however, an etchingreaction gas containing a large amount of the carbon component isgenerated during the etching of the second interlayer insulating film,which facilitates deposition of polymer on the wall and the bottom ofthe first opening. In addition, the carbon component in the secondinterlayer insulating film blocks progress of the etching at the bottom,causing reduction in etching rate toward the bottom. Therefore, with theprogress of the etching toward the bottom of the first opening, a largeramount of polymer is deposited on the wall of the first opening. As aresult, formed is the first opening of which the diameter is smallertoward the bottom.

The first interlayer insulating film contains a smaller proportion ofthe carbon component than the second interlayer insulating film.Therefore, the following phenomenon occurs during plasma etching of thefirst interlayer insulating film. Both the deposition of a polymer filmand the etching proceeds competing with each other at the bottom of thesecond opening. In this occasion, only a comparatively small amount ofan etching reaction gas is generated from the first interlayerinsulating film during the etching thereof, and thus deposition of apolymer film on the wall and the bottom of the second opening is small.This enables a sufficient amount of the carbon component to beeliminated from the first interlayer insulating film at the bottom ofthe second opening, and thus prevents reduction in etching rate towardthe bottom. Therefore, with the progress of the etching toward thebottom of the second opening, only a small amount of polymer isdeposited on the wall of the second opening. As a result, formed is thesecond opening of which the wall is roughly vertical to the bottom face.

In the second fabricating method of a semiconductor device, the plasmaetching is preferably performed with an etching gas containing fluorine,carbon and nitrogen.

The third fabricating method for a semiconductor device of the presentinvention, which embodies the second scheme of the third resolutionprinciple, includes the steps of: depositing an interlayer insulatingfilm represented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z>0) on a substrate;performing first plasma-etching for the interlayer insulating film whileblocking or suppressing a carbon component from being eliminated from asurface portion of the interlayer insulating film, to form a firstopening in the interlayer insulating film, the diameter of the firstopening being smaller toward the bottom end; and performing secondplasma etching for the interlayer insulating film while facilitatingelimination of the carbon component from the surface portion of theinterlayer insulating film, to form a second opening under the firstopening in the interlayer insulating film, the wall of the first openingbeing vertical to the bottom surface.

According to the third fabricating method for a semiconductor device, inthe first plasma etching for the interlayer insulating film, which isperformed while blocking or suppressing the carbon component from beingeliminated from the surface portion of the interlayer insulating film,the following phenomenon occurs. Both the deposition of a polymer filmand the etching proceeds competing with each other at the bottom of thefirst opening. In this occasion, however, since elimination of thecarbon component from the interlayer insulating film is blocked orreduced, progress of the etching is impeded, and thus the etching ratedecreases toward the bottom. Therefore, with the progress of the etchingtoward the bottom, a larger amount of polymer is deposited on the wall.As a result, the first opening of which the diameter is smaller towardthe bottom is formed in the upper part of the interlayer insulatingfilm.

In the second plasma etching for the interlayer insulating film, whichis performed while facilitating elimination of the carbon component fromthe surface portion of the interlayer insulating film, the followingphenomenon occurs. Both the deposition of a polymer film and the etchingproceeds competing with each other at the bottom of the second opening.In this occasion, since the carbon component is sufficiently eliminatedfrom the surface of the interlayer insulating film, the etching ratedoes not decrease with progress of the etching toward the bottom.Therefore, only a small amount of polymer is deposited on the wall incomparison with the progress of the etching toward the bottom. As aresult, the second opening of which the wall is vertical to the bottomface is formed in the lower part of the interlayer insulating film.

In the third fabricating method for a semiconductor device, preferably,the first plasma etching is performed with first etching gas containingfluorine, carbon and nitrogen in which the proportion of nitrogen isrelatively small, and the second plasma etching is performed with asecond etching gas containing fluorine, carbon and nitrogen in which theproportion of nitrogen is relatively large.

(Fourth Resolution Principle)

As described above, the phenomenon that acid generated in the exposedportions of the resist film is deactivated is unique to the chemicalamplification resist film formed on an organic/inorganic hybrid film,and does not occur in the chemical amplification resist film formed on asilicon oxide film. It is not possible to prevent this acid deactivationby increasing the exposure of an energy beam emitted to the resist film.From these facts and others, the acid deactivation is presumed to occuras a result of reaction of acid (H⁺) generated in the exposed portionswith a reactive group contained in the organic/inorganic hybrid film.

In the fourth resolution principle, therefore, a silicon oxide film isinterposed between the organic/inorganic hybrid film and the chemicalamplification resist film for blocking the reaction of acid generated inthe exposed portions with a reactive group contained in theorganic/inorganic hybrid film.

The fourth fabricating method for a semiconductor device of the presentinvention includes the steps of: depositing an interlayer insulatingfilm represented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z>0) on a substrate;forming a silicon oxide film containing no carbon component on the topsurface or a surface portion of the interlayer insulating film; forminga resist film made of a chemical amplification resist material on thesilicon oxide film; and subjecting the resist film to pattern exposureand development to form a resist pattern made of the resist film.

According to the fourth fabricating method for a semiconductor device,the silicon oxide film containing no reaction group exists between theinterlayer insulating film and the resist film made of the chemicalamplification resist material. Therefore, acid generated in exposedportions of the resist film is prevented from reacting with the carboncomponent contained in the interlayer insulating film, and thusprevented from deactivation. This ensures the polarity (solubility to adeveloper) of the exposed portions of the resist film, and thus afterremoval of the exposed portions or non-exposed portions of the resistfilm with a developer, the resultant resist pattern is good in shape.

In the fourth fabricating method for a semiconductor device, the siliconoxide film may be formed by eliminating a carbon component from thesurface portion of the interlayer insulating film.

The fifth fabricating method for a semiconductor device of the presentinvention includes the steps of: depositing an etching stopper film onan interconnection layer formed on a substrate, and then depositing aninterlayer insulating film represented by SiC_(x)H_(y)O_(z) (x>0, y≧0,z>0) on the etching stopper film; forming a contact hole through theinterlayer insulating film; forming a resist pattern made of a chemicalamplification resist material, the resist pattern having an opening forformation of an interconnection groove, and also forming a protectionfilm made of the chemical amplification resist material on the bottom ofthe contact hole for protecting the etching stopper film; andplasma-etching the interlayer insulating film using the resist pattern,to form the interconnection groove in the interlayer insulating film.

According to the fifth fabricating method for a semiconductor device,the protection film made of a chemical amplification resist material isformed on the bottom of the contact hole for protecting the etchingstopper film. With the protection film formed in the contact hole, theinterlayer insulating film is plasma-etched to form an interconnectiongroove therein. Therefore, the portion of the etching stopper filmexposed in the contact hole is prevented from being exposed to theplasma for formation of the interconnection groove and thus is damagedless easily. Using this method, the etching stopper film can be madethin and still can protect the interconnection layer from being stillcan protect the interconnection layer from being exposed to the plasma.It is therefore possible to avoid damaging of the surface of theinterconnection layer or formation of a naturally oxidized film on thesurface of the interconnection layer.

The sixth fabricating method for a semiconductor device of the presentinvention, which corresponds to application of the first and secondresolution principles to a fabrication process of a semiconductordevice, includes the steps of: depositing an etching stopper film on aninterconnection layer formed on a substrate, the etching stopper filmbeing represented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z≧0) in which theproportion of carbon atoms with respect to silicon atoms is relativelylarge; depositing an interlayer insulating film on the etching stopperfilm, the interlayer insulating film being represented bySiC_(x)H_(y)O_(z) (x>0, y≧0, z>0) in which the proportion of carbonatoms with respect to silicon atoms is relatively small; depositing aCMP stopper film on the interlayer insulating film; forming a resistpattern having an opening for formation of a contact hole on the CMPstopper film; transferring the opening of the resist pattern to the CMPstopper film, and then plasma-etching the interlayer insulating filmwhile eliminating a carbon component from a surface portion of theinterlayer insulating film, to form a contact hole through theinterlayer insulating film; after removal of the resist pattern,depositing a conductive film resist pattern, depositing a conductivefilm on the CMP stopper film to fill the contact hole with theconductive film; and removing a portion of the conductive film exposedon the CMP stopper film by CMP, to form a plug made of the conductivefilm.

According to the sixth fabricating method for a semiconductor device, acontact hole is formed through the insulating film by performing plasmaetching while eliminating the carbon component from the surface portionof the interlayer insulating film. Formation of a polymer film isreduced on the surface portion from which the carbon component has beeneliminated. Therefore, the etching rate does not decrease, and thus thecontact hole can be formed through the interlayer insulating film withreliability.

The etching stopper film containing a carbon component in a largeproportion compared with the interlayer insulating film is formed underthe interlayer insulating film. Therefore, once the plasma etching ofthe interlayer insulating film is completed, the following phenomenonoccurs. The etching stopper film containing a larger amount of a carboncomponent is more or less etched and generates an etching reaction gascontaining a carbon component, which is mixed in the plasma. Inaddition, a large amount of the carbon component exists in the etchingstopper film and on the surface thereof. Therefore, a thick polymer filmis deposited on the bottom of the contact hole, and this sharply reducesthe etching rate of the etching stopper film. Thus, the etching stopperfilm in which the proportion of the carbon component is relatively largeserves as the etching stopper film when the interlayer insulating filmis plasma-etched to form a contact hole.

In addition, the etching stopper film is made of an insulating filmhaving a low specific dielectric constant, and thus enables largereduction in the specific dielectric constant between the lower andupper interconnections, compared with a silicon nitride film having alarge specific dielectric constant.

Moreover, the CMP stopper film is interposed between the interlayerinsulating film and the conductive film for formation of the plug. Theinterlayer insulating film is therefore protected from being subjectedto CMP when the portion of the conductive film exposed on the CMPstopper film is removed by CMP. Therefore, the interlayer insulatingfilm is prevented from being damaged even though it is made of anorganic/inorganic hybrid film that is susceptible to CMP.

The seventh fabricating method for a semiconductor device of the presentinvention, which corresponds to of the first and second resolutionprinciples to a fabrication process of multilayer interconnectionshaving a dual damascene structure, includes the steps of: depositing anetching stopper film on a lower interconnection formed on a substrate,the etching stopper film being represented by SiC_(x)H_(y)O_(z) (x>0,y≧0, z≧0) in which the proportion of carbon atoms with respect tosilicon atoms is relatively large; depositing an interlayer insulatingfilm on the etching stopper film, the interlayer insulating film beingrepresented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z>0) in which the proportionof carbon atoms with respect to silicon atoms is relatively small;depositing a CMP stopper film on the interlayer insulating film; forminga first resist pattern having an opening for formation of a contact holeon the CMP stopper film; transferring the opening of the first resistpattern to the CMP stopper film, and then plasma-etching the interlayerinsulating film while eliminating a carbon component from a surfaceportion of the second organic/inorganic hybrid film, to form a contacthole through the interlayer insulating film; after removal of the firstresist pattern, forming a second resist pattern having an opening forformation of an interconnection groove on the CMP stopper film;transferring the opening of the second resist pattern to the CMP stopperfilm, and then plasma-etching the interlayer insulating film whileeliminating a carbon component from a surface portion of the interlayerinsulating film, to form an interconnection groove in the interlayerinsulating film; depositing a conductive film on the CMP stopper film tofill the contact hole and the interconnection groove with the conductivefilm; and removing a portion of the conductive film exposed on the CMPstopper film by CMP, to form a plug and an upper interconnection made ofthe conductive film.

According to the seventh fabricating method for a semiconductor device,as in the sixth fabricating method, a contact hole is formed through theinterlayer insulating film by performing plasma etching whileeliminating the carbon component from the surface portion of theinterlayer insulating film. Therefore, the etching rate does notdecrease, and thus the contact hole and the interconnection groove canbe formed in the interlayer insulating film with reliability.

The etching stopper film in which the proportion of the carbon componentis relatively large compared with the interlayer insulating film servesas the etching stopper film when the interlayer insulating film isplasma-etched to form a contact hole and an interconnection groove.

In addition, the etching stopper film is made of an insulating filmhaving a low specific dielectric constant, and thus enables largereduction in the specific dielectric constant between the lower andupper interconnection, compared with a silicon nitride film having alarge specific dielectric constant.

Moreover, the CMP stopper film is interposed between the interlayerinsulating film and the conductive film for formation of the plug andthe upper interconnection. The interlayer insulating film is thereforeprotected from being subjected to CMP when the portion of the conductivefilm exposed on the CMP stopper film is removed by CMP. Therefore, theinterlayer insulating film is prevented from being damaged even thoughit is made of an organic/inorganic hybrid film that is susceptible toCMP.

Thus, it is ensured to reduce the specific dielectric constant betweenthe lower and upper interconnections in multilayer interconnectionshaving a dual damascene structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the entire construction of a plasmaprocessing apparatus used in embodiments of the present invention.

FIG. 2 is a flowchart of an etching method of the first embodiment ofthe present invention.

FIG. 3 is a cross-sectional view for description of a mechanism ofreforming and then etching a surface portion of an organic/inorganichybrid film in the etching method of the first embodiment of the presentinvention.

FIG. 4 is a view showing the timing at which a gas containing a N₂component and CF gas are fed in the first embodiment of the presentinvention.

FIGS. 5( a) and 5(b) are views showing the relationships between thedistance in the depth direction and the atomic concentration obtainedfrom XPS analysis of film types a and b, respectively, of theorganic/inorganic hybrid film.

FIGS. 6( a) and 6(b) are views showing the relationships between thedistance in the depth direction and the atomic concentration obtainedfrom XPS analysis of film types c and d, respectively, of theorganic/inorganic hybrid film.

FIG. 7 is a view showing the relationship between the distance in thedepth direction and the atomic concentration for a film obtained byreforming the film type c of the organic/inorganic hybrid film usingNH₃/N₂ gas.

FIG. 8 is a flowchart of an etching method of the second embodiment ofthe present invention.

FIG. 9 is a view showing the timing at which a gas containing a N₂component and CF gas are fed in the second embodiment of the presentinvention.

FIG. 10( a) is a cross-sectional view illustrating a fabricating methodfor a semiconductor device of the third embodiment of the presentinvention, and FIG. 10( b) is a cross-sectional view illustrating afabricating method for a semiconductor device of a modification of thethird embodiment of the present invention.

FIGS. 11( a) through 11(c) are cross-sectional views of process steps ofa fabricating method for a semiconductor device of the fourth embodimentof the present invention.

FIGS. 12( a) through 12(c) are cross-sectional views of process steps ofa fabricating method for a semiconductor device of the fifth embodimentof the present invention.

FIG. 13 is a view showing the timing at which a gas containing a N₂component and CF gas are fed in the fifth embodiment of the presentinvention.

FIGS. 14( a) through 14(c) are cross-sectional views of process steps ofa fabricating method for a semiconductor device of the sixth embodimentof the present invention.

FIGS. 15( a) through 15(d) are cross-sectional views of process steps ofthe fabricating method for a semiconductor device of the sixthembodiment of the present invention.

FIGS. 16( a) through 16(c) are cross-sectional views of process steps ofa fabricating method for a semiconductor device of the seventhembodiment of the present invention.

FIGS. 17( a) through 17(c) are cross-sectional views of process steps ofthe fabricating method for a semiconductor device of the seventhembodiment of the present invention.

FIGS. 18( a) through 18(d) are cross-sectional views of process steps ofthe fabricating method for a semiconductor device of the seventhembodiment of the present invention.

FIGS. 19( a) through 19(c) are cross-sectional views of process steps ofa fabricating method for a semiconductor device of the eighth embodimentof the present invention.

FIGS. 20( a) through 20(c) are cross-sectional views of process steps ofthe fabricating method for a semiconductor device of the eighthembodiment of the present invention.

FIGS. 21( a) through 21(c) are cross-sectional views of process steps ofa fabricating method for a semiconductor device of the secondmodification of the eighth embodiment of the present invention.

FIGS. 22( a) through 22(d) are cross-sectional views of process steps ofthe first conventional fabricating method for a semiconductor device.

FIGS. 23( a) through 23(d) are cross-sectional views of process steps ofthe second conventional fabricating method for a semiconductor device.

FIGS. 24( a) and 24(b) are cross-sectional views for description of aproblem occurring when a chemical amplification resist film is formed onan interlayer insulating film made of an organic/inorganic hybrid film.

FIG. 25 is a cross-sectional view for description of the problemoccurring when a chemical amplification resist film is formed on aninterlayer insulating film made of an organic/inorganic hybrid film.

FIG. 26( a) is a cross-sectional view of a contact hole formed bydry-etching an interlayer insulating film made of a silicon oxide filmwith an etching gas containing fluorine and carbon, and FIG. 26( b) is across-sectional view of a contact hole formed by dry-etching aninterlayer insulating film made of an organic/inorganic hybrid film withan etching gas containing fluorine and carbon.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(Plasma Processing Apparatus)

Hereinafter, embodiments of the etching methods according to the presentinvention will be described. First, as a precondition for theembodiments, a plasma processing apparatus used for etching will bedescribed with reference to FIG. 1.

FIG. 1 shows a cross-sectional structure of the plasma processingapparatus. A lower electrode 11, which is used as a sample mount, isplaced in a lower portion of a reaction chamber 10 and holds asemiconductor substrate 12 by electrostatic adsorption. An upperelectrode 13 is placed in the upper portion of the reaction chamber 10to face the lower electrode 11. An etching gas is fed into the reactionchamber 10 via a gas inlet 14 formed at the upper electrode 13. The gasinside the reaction chamber 10 is discharged by a vacuum pump 15disposed under the reaction chamber 10.

A plasma induction coil 17 is placed on the reaction chamber 10 with aninsulator 16 therebetween. An end of the plasma induction coil 17 isconnected to a first high-frequency source 19 via a first matchingdevice 18, while the other end is grounded. The lower electrode 11 isconnected to a second high-frequency source 21 via a second matchingdevice 20.

When a first high-frequency power is applied to the plasma inductioncoil 17 from the first high-frequency source 19, a high-frequencyinduced magnetic field is generated inside the reaction chamber 10, sothat the etching gas fed in the reaction chamber 10 becomes plasma. Whena second high-frequency power is applied to the lower electrode 11 fromthe second high-frequency source 21, the plasma generated in thereaction chamber 10 is directed to the lower electrode 11, that is, tothe semiconductor substrate 12, which is thus exposed to the plasma.

First Embodiment

A plasma etching method of the first embodiment of the present inventioncarried out using the plasma processing apparatus described above willbe described with reference to FIGS. 1, 2, 3, 4, 5(a), 5(b), 6(a), 6(b),and 7.

First, as shown in FIG. 3, an interconnection layer 102 made of analuminum film, a copper film, an alloy film of aluminum or copper as amain component, or the like is embedded in an insulating film 101deposited on a semiconductor substrate 100. Note that, althoughillustration is omitted in FIG. 3, the sides and the bottom of theinterconnection layer 102 are coated with barrier metal that preventsmetal atoms constituting the interconnection layer 102 from dispersinginto the insulating film 101.

Thereafter, an etching stopper film 103 is deposited on the entire topsurface of the semiconductor substrate 100 including the interconnectionlayer 102. The etching stopper film 103, which is made of a siliconnitride film, for example, protects the interconnection layer 102 andalso serves as an etching stopper. The etching stopper film 103 isespecially required when a dual damascene interconnection structure isformed, and prevents the interconnection layer 102 from being oxidizedwith an etching gas during etching of an organic/inorganic hybrid film104 described below. The etching stopper film 103 also prevents theetching apparatus from being polluted with metal.

The organic/inorganic hybrid film 104 represented by SiC_(x)H_(y)O_(z)(>0, y≧0, z>0) is then deposited on the etching stopper film 103 using aknown CVD apparatus. A resist pattern 105 having openings for formationof contact holes is formed on the organic/inorganic hybrid film 104.

As the gas for deposition of the organic/inorganic hybrid film 104,usable is a mixed gas of a material gas such as tetramethylsilane(Si(CH₃)₄), dimethyl.dimethylsiloxane (Si(CH₃)₂(—O—CH₃)₂),monomethylsilane (SiH₃(CH₃)), or Hexamethyldisiloxane(Si(CH₃)₃—O—Si(CH₃)₃) and an additive gas such as N₂O. In the firstembodiment, a mixed gas of hexamethyldisiloxane (HMDSO) and N₂O was fedinto the CVD apparatus, to deposit the organic/inorganic hybrid film 104made of a hexamethyldisiloxane film on the semiconductor substrate 100that is kept at 300° C.

Thereafter, in step SA1 shown in FIG. 2, the resultant semiconductorsubstrate 100 is placed in the reaction chamber 10 of the plasma etchingapparatus shown in FIG. 1. In step SA2, the semiconductor substrate 100is fixed to the lower electrode 11 by electrostatic adsorption.

In step SA3, an etching gas containing fluorine, carbon and nitrogen isfed into the reaction chamber 10 in a manner as shown in FIG. 4. Anexample of the etching gas containing fluorine, carbon and nitrogen is amixed gas of a fluorocarbon (CF) gas normally used for etching of a SiO₂film and a N₂ gas. Details of the etching gas containing fluorine,carbon and nitrogen will be described later.

In step SA4, the first high-frequency power is applied to the plasmainduction coil 17 from the first high-frequency source 19, to generateplasma between the lower electrode 11 and the upper electrode 13. Also,the second high-frequency power is applied to the lower electrode 11from the second high-frequency source 21. With this application, theetching species in the plasma are attracted to the semiconductorsubstrate 100. As a result, in step SA5, the organic/inorganic hybridfilm 104 is plasma-etched using the resist pattern 105 as a mask.

Once the organic/inorganic hybrid film 104 has been etched to apredetermined depth, in step SA6, the application of the high-frequencyvoltages to the upper electrode 13 and the lower electrode 11 and thefeeding of the etching gas are stopped, to finish the etching.

Hereinafter, an example of the etching gas used for the plasma etchingof the organic/inorganic hybrid film 104, as well as the etchingconditions thereof, will be described.

First, an etching gas having a volume flow ratio of

-   -   C₄F₈:CH₂F₂:Ar:CO:N₂=2:1:10:5:0.5        is fed via the gas inlet 14 into the reaction chamber 10 that is        kept at a pressure of 2.6 Pa. The first high-frequency power of        1500 W at 13.56 MHz, for example, is applied to the plasma        induction coil 17 from the first high-frequency source 19, to        generate plasma between the lower electrode 11 and the upper        electrode 13. Also, the second high-frequency power of 1400 W at        4 MHz, for example, is applied to the lower electrode 11 from        the second high-frequency source 21, to attract the etching        species in the plasma to the semiconductor substrate 100 to        thereby enable plasma etching.

By the plasma etching described above, the etching species such as N₂contained in the plasma are attracted to the bottom of a contact hole104 a, and reacts with carbon atoms and hydrogen atoms existing on thebottom. Thus, on the bottom of the contact hole 104 a, a reformed layer(oxidized region) 104 b where the carbon component has been eliminatedis formed. At this time, a volatile reaction product such as HCN or CNis generated. By this reformation, the composition of the bottom portion(reformed layer 104 b) of the contact hole 104 a is close to thecomposition of SiO₂. This means that the bottom of the contact hole 104a is nicely etched with the etching species such as CF_(x) contained inthe plasma, while a volatile reaction product such as SiF, CO₂, CHF₃, orCH₄ is generated. As a result, the etching rate at the bottom of thecontact hole 104 b in the organic/inorganic hybrid film 104 is roughlythe same as the etching rate at a silicon oxide (SiO₂) film containingno carbon component.

X-ray photoelectron spectroscopy (XPS) analysis was performed for theorganic/inorganic hybrid film 104 immediately after the depositionthereof and when plasma processing was performed with NH₃/N₂ gas. Theresults of the analysis are as follows.

FIGS. 5( a), 5(b), 6(a), and 6(b) show the results of XPS analysis ofthe four types (film types a, b, c, and d) of the organic/inorganichybrid film 104 that were formed under different deposition conditions.In each graph, the x-axis represents the distance in the depth direction(corresponding to the sputtering time) and the y-axis represents theatomic concentration. FIGS. 4( a), 4(b), 5(a), and 5(b) show the resultsof film types a, b, c, and d, respectively. The compositions of the fourfilm types a, b, c, and d are as follows: the silicon component occupiesabout 30%, the oxygen component about 25 to 45%, the carbon componentabout 17 to 37%, and the nitrogen component about 5% or less. From theXPS analysis results and in consideration of the material gas for filmformation, it is presumed that SiC, SiN, and CHX (x=1 to 3) are capturedin the network of SiO_(x) (x=1 to 3) where the amount of CH_(x) capturedis the largest.

FIG. 7 shows the relationship between the distance in the depthdirection and the atomic concentration for the film type c shown in FIG.6( a) (containing about 30% of each of the silicon component, the carboncomponent, and the oxygen component, and about 5% of the nitrogencomponent) of the organic/inorganic hybrid film 104 observed when plasmaprocessing was performed using plasma of a mixed gas of ammonia gas andnitrogen gas. As is found from FIG. 7, in the surface portion of theorganic/inorganic hybrid film 104 (portion having a depth of about. 20nm from the surface), the oxygen component increases to about 65% whilethe carbon component decreases to 5% or less, with the silicon componentand the nitrogen component being kept unchanged. From these results, itis found that the surface portion of the organic/inorganic hybrid film104 was reformed to have a composition close to that of a silicon oxide(SiO₂) film. Also found is that it is only the surface portion of theorganic/inorganic hybrid film 104 that was reformed with the otherportion thereof being kept non-reformed. Therefore, the specificdielectric constant of the organic/inorganic hybrid film 104 remainslow.

Hereinafter, the etching gas used for the plasma etching method will bedescribed.

Normally, a main etching gas used for plasma etching of a SiO₂ film is aCF gas such as CF₄, C₂F₆, C₂F₄, C₃F₆, C₃F₈, C₄F₄F₆, C₄F₈ (straight-chainor cyclic), and C₅F₈ (straight-chain or cyclic). A CHF gas such as CHF₃,CH₂F₂, and CH₃F is also used as a main etching gas or an added gas forplasma etching of the SiO₂ film. In general, any of these main etchinggases is seldom used singularly or in combination with other mainetching gases only. Instead, a rare gas (He, Ar, Ne, Kr, Xe, etc.) or O₂gas is often mixed in the main etching gas. The rare gas is mixed forthe purposes of diluting the etching gas, increasing the discharge rateof the gas in the reaction chamber, and controlling the electrontemperature of the plasma, among others. The O₂ gas is often added forthe purpose of removing a polymer film appropriately in the case thatthe polymer film may possibly be excessively formed on the wafer surfaceif only the main etching gas is used.

Moreover, Co, CO₂, SO, SO₂, and the like may sometimes be added for thepurpose of improving the etching ability of a resist pattern as anetching mask for the SiO₂ film or improving the etching selection ratioof the SiO₂ film to an underlying film (ratio of the etching rate of theSiO₂ film to that of an underlying film). By using a gas obtained bycombining the gases described above, it is possible to perform suitableetching for the SiO₂ film that meets the requirements in the process.

However, any of combinations of gasses described above fails to suitablyetch an organic/inorganic hybrid SiO₂ film. In order to attain etchingsuitable for an organic/inorganic hybrid SiO₂ film, the etching methodof the present invention is inevitably required.

The etching method of the first embodiment is based on the mechanismthat etching is performed by repeating alternately in a microscopicsense (simultaneously in a macroscopic sense) the processes of: reactingan organic component in an organic/inorganic hybrid film withnitrogen-containing molecules on the etching reaction surface of theorganic/inorganic hybrid film and removing a reaction product; andreacting silicon in the organic/inorganic hybrid film with a gascontaining fluorine and carbon and removing a reaction product.

As described above, as the etching gas used in the first embodiment,usable is a gas including a main etching gas capable of etching a SiO₂film, which is either a gas containing fluorine and carbon or a gascontaining fluorine, carbon, and hydrogen, into which a gas containing anitrogen component is mixed.

Examples of the gas containing a nitrogen component mixed in the mainetching gas include a single gas of nitrogen (N₂), compounds of nitrogenand hydrogen (NH₃, N₂H₂, etc.), compounds of nitrogen and oxygen (NO,NO₂, N₂O, N₂O₃, etc.), compounds of nitrogen and carbon (C₂N₂, etc.),compounds of nitrogen and fluorine (NF₃, etc.), and compounds ofnitrogen, oxygen, and fluorine (NOF, NO₂F, etc.).

The compounds of nitrogen and carbon (C₂N₂, etc.), with which the effectof the present invention is obtainable, are however not preferable fromthe standpoint of safety because in the event of gas leakage, thecompounds will react with water in the atmosphere and generate prussicacid gas (HCN).

As described in the “SUMMARY OF THE INVENTION”, Japanese Laid-OpenPatent Publication No. 9-263050 describes a method for etching an“inorganic” SiO₂ film containing fluoride or fluoride/nitrogen with anetching gas that is a mixture of a fluorocarbon gas and a gas of acompound of nitrogen and hydrogen.

The feature of the etching method described in Japanese Laid-Open PatentPublication No. 9-263050 is as follows. By generating plasma from theetching gas that is a mixture of a fluorocarbon gas and a gas of acompound of nitrogen and hydrogen, fluorine dissociated from thefluorocarbon and fluorine released from the fluorine-containing“inorganic” SiO₂ film are bound with nitrogen or hydrogen. In this way,excessive generation of fluorine is suppressed. By this mechanism, theratio of the etching rate of the “inorganic” SiO₂ film to that of thephotoresist mask or the underlying substrate is improved, that is, theetching selection ratio is improved.

As is apparent from the above, the mechanism utilized by the etchingmethod for an organic/inorganic hybrid film of the present invention iscompletely different from the etching method disclosed in JapaneseLaid-Open Patent Publication No. 9-263050.

From the standpoint of eliminating the carbon component form the surfaceportion of the organic/inorganic hybrid SiO₂ film, the reaction on theetching reaction surface of the organic/inorganic hybrid SiO₂ film isfacilitated more efficiently by adding both nitrogen gas and hydrogengas than by adding only nitrogen gas. The reason is that by addingnitrogen gas and hydrogen gas, there occurs a reaction changing carbonto HCN or the like that is highly volatile and therefore carbon iseasily eliminated. In other words, carbon can be eliminated moreefficiently by adding nitrogen gas and hydrogen gas to the etching gasthan by adding only nitrogen gas. Thus, by adding hydrogen gas to theetching gas containing fluorine, carbon and nitrogen, it is possible toenhance the efficiency of elimination of the carbon component.

From the standpoint of enabling supply of nitrogen and hydrogen in theplasma, the effect obtained by mixing a nitrogen-containing gas andhydrogen gas separately into the etching gas containing fluorine andcarbon is substantially the same as the effect obtained by mixing a gasof a compound of nitrogen and hydrogen into the etching gas.

As described above, the ability of eliminating the carbon componentincreases by mixing nitrogen and hydrogen into a gas containing fluorineand carbon in the etching method for an organic/inorganic hybrid film.Note that there is a danger of causing explosion and the like ifhydrogen gas and oxygen gas are simultaneously added to a gas containingfluorine, carbon and nitrogen. Therefore, if importance is put onsafety, no oxygen gas should preferably be added when hydrogen gas isadded.

The fluorocarbon gas and the hydrofluorocarbon gas were used exemplifiedabove as the etching gas containing fluorine and carbon mainly used foretching of the inorganic SiO₂ film.

In the etching method of the present invention, gases that exhibit goodproperties in etching of the inorganic SiO₂ film, such as HFE(hydrofluoro-ether) or HFO (hydrofluoro cyclized olefin), may be used asthe etching gas containing fluorine and carbon. These gases haverecently received attention as etching gases contributing to preventionof global warming. The etching method of the present invention can alsobe attained by mixing a nitrogen-containing gas into these gases.

By mixing a gas enabling supply of oxygen in the plasma, such as CO andCO₂, into the etching gas containing fluorine, carbon and nitrogen, thesurface portion of the organic/inorganic hybrid film 104 can be oxidizedor reformed efficiently.

In the case that the gas containing a nitrogen component is replacedwith oxygen gas, the carbon component existing in the surface portion ofthe organic/inorganic hybrid film 104 reacts with the oxygen component,generating carbon monoxide and carbon dioxide. The surface portion istherefore oxidized and thus reformed. However, by adding oxygen gas tothe etching gas, the etching rate of the resist pattern 105 increases,thereby reducing the etching selection ratio of the organic/inorganichybrid film 104 to the resist pattern 105. In addition, with anincreased etching rate, the resist pattern 105 itself is etched, andthus the size of the openings of the resist pattern 105 greatly varies.This makes it difficult to form the fine contact holes 104 a through theorganic/inorganic hybrid film 104 with high size precision.

Thus, in the first embodiment, the organic/inorganic hybrid film 104 isplasma-etched with an etching gas containing fluoride, carbon andnitrogen. Therefore, the organic/inorganic hybrid film 104 can be etchedat an etching rate roughly equal to that of a silicon oxide film, andyet can maintain the properties thereof such as the specific dielectricconstant and also can secure a good etching selection ratio with respectto the resist pattern 105.

The reformation of the surface portion of the organic/inorganic hybridfilm 104 includes removing carbon atoms or hydrogen atoms from thesurface portion to obtain a composition close to that of the SiO₂ film.This is accompanied by increase of the specific dielectric constant.

To avoid the above problem, during the etching for the entireorganic/inorganic hybrid film 104, it is preferable to use an etchinggas containing fluorine, carbon and nitrogen before the etching entersits final stage. At the final stage of the etching, an etching gascontaining fluorine and carbon but containing no nitrogen is preferablyused. In this way, the organic/inorganic hybrid film 104 can be etchedat a high etching rate while the surface portion thereof is beingreformed before the final stage of the etching. At the final stage ofthe etching, the already-reformed surface portion can be etched withoutincreasing the specific dielectric constant. Thus, as the entire etchingprocess, the etching rate can be improved without increasing thespecific dielectric constant.

Second Embodiment

A plasma etching method of the second embodiment of the presentinvention carried out using the plasma processing apparatus describedabove will be described with reference to FIGS. 1, 8, and 9.

First, as in the first embodiment, an interconnection layer is formed ona semiconductor substrate. An etching stopper film is deposited over theentire semiconductor substrate including the interconnection layer. Anorganic/inorganic hybrid film represented by SiC_(x)H_(y)O_(z) (x>0,y≧0, z≧0) is deposited on the etching stopper film, and a resist patternis formed on the organic/inorganic hybrid film.

Thereafter, in step SB1 shown in FIG. 8, the resultant semiconductorsubstrate is placed in the reaction chamber 10 of the plasma etchingapparatus. In step SB2, the semiconductor substrate is fixed to thelower electrode 11.

In step SB3, a reformation gas and an etching gas are fed into thereaction chamber 10. The kinds and the ways of feeding of thereformation gas and the etching gas are to be described with referenceto step SB6.

In step SB4, the first high-frequency power is applied to the plasmainduction coil 17 from the first high-frequency source 19, to generateplasma between the lower electrode 11 and the upper electrode 13. Also,the second high-frequency power is applied to the lower electrode 11from the second high-frequency source 21. With this application, theetching species in the plasma are attracted to the semiconductorsubstrate 100. As a result, in step SB5, the organic/inorganic hybridfilm is plasma-etched.

In step SB6, the feeding of the reformation gas and the etching gas isalternately switched so that the organic/inorganic hybrid film isalternately reformed and etched. Specifically, as shown in FIG. 9,first, a nitrogen-containing gas is fed as the reformation gas to reform(oxidize) the surface portion of the organic/inorganic hybrid film. Thefeeding of the nitrogen-containing gas is then stopped, and a CF gas,for example, is fed as the etching gas containing fluorine and carbon toetch the surface portion of the organic/inorganic hybrid film.Thereafter, the reformation process using the nitrogen-containing gasand the etching process using the CF gas are repeated alternately. Notethat in the process of reforming the surface portion of theorganic/inorganic hybrid film, it is possible to reduce the secondhigh-frequency power applied to the lower electrode 11 from the secondhigh-frequency source 21.

Once the organic/inorganic hybrid film has been etched to apredetermined depth, in step SB7, the application of the high-frequencyvoltages to the upper electrode 13 and the lower electrode 11 and thefeeding of the etching gas are stopped, to finish the etching.

As described above, the etching method of the second embodiment is basedon the mechanism that etching is performed by repeating alternately in amacroscopic sense the processes of: reacting an organic component in theorganic/inorganic hybrid film with nitrogen-containing molecules on theetching reaction surface of the organic/inorganic hybrid film andremoving a reaction product; and reacting silicon in theorganic/inorganic hybrid film with a gas containing fluorine and carbonand removing a reaction product. In this etching method, the impetus forthe process of reacting an organic component in the organic/inorganichybrid film with nitrogen-containing molecules is nitrogen and anitrogen compound generated in the plasma from the gas containing anitrogen component. Likewise, the impetus for the process of reactingsilicon in the organic/inorganic hybrid film with the gas containingfluorine and carbon is fluorine and CF molecules generated in the plasmafrom the gas containing fluorine and carbon.

In view of the above, in the second embodiment, the gas containing anitrogen component may be used in the process of reacting an organiccomponent in the organic/inorganic hybrid film with nitrogen-containingmolecules, and the etching gas containing fluorine and carbonconventionally used for etching of a SiO₂ film may be used in theprocess of reacting silicon in the organic/inorganic hybrid film withthe gas containing fluorine and carbon.

In the second embodiment, also, in the process of reacting an organiccomponent in the organic/inorganic hybrid film with nitrogen-containingmolecules, it is effective to use plasma obtained by adding nitrogen andhydrogen. For example, a mixed gas of H₂ and N₂, NH₃ gas, or the like ispreferably added to the gas containing fluorine and carbon.

In the second embodiment, the reformation process using thenitrogen-containing gas (N₂ gas) and the etching process using the gascontaining fluorine and carbon (CF gas) are repeated alternately.Therefore, a carbide generated by reaction between the CF gas and theSiC_(x)H_(y)O_(z) film is prevented from reacting with an nitride as anetching species. As a result, the reformation of the surface portionwith the nitrogen-containing gas is made efficiently, and the etching ofthe reformed surface portion with the CF gas is made efficiently.

The etching method of the second embodiment is also effective in thecase that the processing conditions are greatly different between thereformation process and the etching process, such as the case that thepreferred gas pressure for the reformation using the nitrogen-containinggas (N₂ gas) is different from the preferred gas pressure for theetching using the gas containing fluorine and carbon (CF gas).

As described above, the reformation of the surface portion of theorganic/inorganic hybrid film is accompanied by increase in specificdielectric constant. Therefore, the etching process should preferably bethe final process in the repetition of the reformation process and theetching process. Also, in the final etching process, the reformedportion should preferably be removed to suppress increase in specificdielectric constant.

Note however that in the case of etching for formation of a contact holethrough the organic/inorganic hybrid film on the etching stopper film,the reformed layer (that is, the bottom of the contact hole) is finallyremoved. Therefore, no increase of the specific dielectric constantoccurs.

Third Embodiment

A semiconductor device and a fabricating method therefor as the thirdembodiment of the present invention will be described with reference toFIG. 10( a).

As shown in FIG. 10( a), first, an interconnection layer 202 made of acopper film, an alloy film of copper as a main component, or the like isembedded in an insulating film 201 deposited on a semiconductorsubstrate 200. Although illustration is omitted in FIG. 10( a), thesides and the bottom of the interconnection layer 202 are coated withbarrier metal for prevention of metal atoms constituting theinterconnection layer 202 from diffusing into the insulating film 201.

An etching stopper film 203 is then deposited on the entire surface ofthe semiconductor substrate 200 including the interconnection layer 202by plasma CVD, for example. The etching stopper film 203 is made of afirst organic/inorganic hybrid film represented by SiC_(x)H_(y)O_(z)(x>0, y≧0, z≧0) in which the proportion of the carbon component isrelatively large.

Subsequently, an interlayer insulating film 204 is deposited on theentire surface of the etching stopper film 203 by plasma CVD, forexample. The interlayer insulating film 204 is made of a secondorganic/inorganic hybrid film represented by SiC_(x)H_(y)O_(z) (x>0,y≧0, z>0) in which the proportion of the carbon component is relativelysmall.

As the film formation gas for deposition of the etching stopper film 203and the interlayer insulating film 204, usable is a mixed gas of amaterial gas such as tetramethylsilane (Si(CH₃)₄),dimethyl.dimethylsiloxane (Si(CH₃)₂(—O—CH₃)₂), monomethylsilane (SiH₃(CH₃)), or Hexamethyldisiloxane (Si(CH₃)₃—O—Si(CH₃)₃) and an additivegas such as N₂O. in the third embodiment, a mixed gas ofhexamethyldisiloxane (HMDSO) and N₂O was fed into a CVD apparatus, todeposit the interlayer insulating film 204 on the semiconductorsubstrate 200 that is kept at 300° C.

The feature of the third embodiment is that the proportion of the carboncomponent contained in the first organic/inorganic hybrid filmconstituting the etching stopper film 203 is larger than the proportionof the carbon component contained in the second organic/inorganic hybridfilm constituting the interlayer insulating film 204.

The proportion of the carbon component in the etching stopper film 203can be made larger than that in the interlayer insulating film 204 inthe following manner, for example. The same kind of the material gas(for example, HMDSO) is used as the main component. The proportion ofthe additive gas (for example, N₂O) contained in the film formation gasfor deposition of the etching stopper film 203 is reduced, while theproportion of the additive gas contained in the film formation gas fordeposition of the interlayer insulating film 204 is increased.Alternatively, a film formation gas including a material gas containingan increased amount of the carbon component may be used for depositionof the etching stopper film 203, while a film formation gas including amaterial gas containing a reduced amount of the carbon component may beused for deposition of the interlayer insulating film 204.

Thereafter, a resist pattern 205 having openings for formation ofcontact holes is formed on the interlayer insulating film 204. Theinterlayer insulating film 204 is then plasma-etched using the resistpattern 205 as a mask.

The same etching gas and etching conditions as those used in the firstembodiment are applied for the plasma etching of the interlayerinsulating film 204. That is, an etching gas having a volume flow ratioof:

-   -   C₄F₈:CH₂F₂:Ar:CO:N₂=2:1:10:5:0.5        is fed into the reaction chamber 10 that is kept at a pressure        of 2.6 Pa via the gas inlet 14. The first high-frequency power        of 1500 W at 13.56 MHz, for example, is applied to the plasma        induction coil 17 from the first high-frequency source 19, to        generate plasma between the lower electrode 11 and the upper        electrode 13. Also, the second high-frequency power of 1400 W at        4 MHz, for example, is applied to the lower electrode 11 from        the second high-frequency source 21, to attract the etching        species in the plasma to the semiconductor substrate 100 to        thereby enable plasma etching.

Thus, as in the first embodiment, the etching species such as N₂ in theplasma are attracted to the bottom of the contact hole 204 a and reactwith carbon atoms or hydrogen atoms existing on the bottom. As a result,a reformed layer (oxidized region) where the carbon component has beeneliminated is formed on the bottom of the contact hole 204 a, and thusthe reformed bottom of the contact hole 204 b is nicely etched with theetching species such as CF_(x) contained in the plasma.

Once the etching of the interlayer insulating film 204 has beencompleted and the underlying etching stopper film 203 is exposed in thecontact hole 204 a, the etching is blocked due to the following reason.The proportion of the carbon component contained in the etching stopperfilm 203 is larger than the proportion of the carbon component containedin the interlayer insulating film 204 as described above. Therefore,when the etching stopper film 203 is etched as the etching proceeds, anetching reaction gas containing the carbon component is generated,resulting in deposition of a thick polymer film. In addition, the carboncomponent of the etching stopper film 203, as well as an excess of thecarbon component of the polymer film, is accumulated on the etchingstopper film 203, thereby blocking the progress of the etching. Thissharply decreases the etching rate, and thus the etching stops at thesurface of the etching stopper film 203.

The etching gas contains a fluorine component for cleaving Si—O bonds asdescribed above. This fluorine component in the etching gas is scavengedby the carbon component contained in the etching stopper film 203. Morespecifically, the fluorine contained in the etching gas reacts with acarbide such as a methyl group contained in the etching stopper film203, to produce a fluorocarbon compound. By this reaction, the amount ofthe fluorine component contained in the etching gas is reduced, andtherefore cleaving of the Si—O bonds in the etching stopper film 203becomes less easy. This sharply decreases the etching rate, and thus theetching stops at the surface of the etching stopper film 203.

Thus, in the third embodiment, the etching stopper film 203 made of thesecond organic/inorganic hybrid film having a relatively largeproportion of the carbon component is formed under the interlayerinsulating film 204 made of the first organic/inorganic hybrid filmhaving a relatively small proportion of the carbon component. Such anetching stopper film 203 can serve as the etching stopper for theinterlayer insulating film 204, and moreover can provide a significantlysmall specific dielectric constant compared with the conventionaletching stopper film made of a silicon nitride.

In the third embodiment, if the etching stopper film 203 contains anoxygen component, the interconnection layer 202 may possibly be oxidizedwith the oxygen component although slightly. Therefore, when the etchingstopper film 203 is made of an organic/inorganic hybrid film representedby SiC_(x−)H_(y)O_(z) (x>0, y≧0, z>0), the film is preferably aninsulating film containing no oxygen component (that is, z=0).

In the third embodiment, the thickness of the etching stopper film 203is preferably about 50 nm when the thickness of the interlayerinsulating film 204 is about 800 nm. By this setting, a sufficientetching selection ratio can be secured for the etching stopper film 203.

(Modification of the Third Embodiment)

A semiconductor device and a fabricating method therefor as amodification of the third embodiment of the present invention will bedescribed with reference to FIG. 10( b).

The feature of the modification of the third embodiment is that, asshown in FIG. 10( b), a protection film 206 made of a silicon nitridefilm, a silicon carbide film, or the like having a thickness of 10 nm,for example, is formed between the interconnection layer 202 and theetching stopper film 203.

As described above, if the etching stopper film 203 is made of anorganic/inorganic hybrid film containing an oxygen component, theinterconnection layer 202 may possibly be oxidized with the oxygencomponent although slightly.

In the modification of the third embodiment, the protection layer 206containing no oxygen component is provided between the interconnectionlayer 202 and the etching stopper film 203. The interconnection layer202 is therefore prevented from being oxidized reliably even when theetching stopper film 203 contains an oxygen component.

The thickness of the protection film 206 is so small that increase inthe specific dielectric constant between the lower and upperinterconnections is prevented even when the protection film 206 has amore or less high specific dielectric constant.

In the third embodiment including the modification thereof, theinterconnection layer 202 was of an embedded type. In the case that theinterconnection layer 202 is formed by patterning a conductive film,also, the effects of the third embodiment and the modification thereofcan be obtained.

Fourth Embodiment

A semiconductor device and a fabricating method therefor of the fourthembodiment will be described with reference to FIGS. 11( a) to 11(c).

First, as shown in FIG. 11( a), an interconnection layer 302 made of acopper film, an alloy film of copper as a main component, or the like isembedded in an insulating film 301 deposited on a semiconductorsubstrate 300.

An etching stopper film 303 is then deposited on the entire surface ofthe interconnection layer 302 by plasma CVD, for example. The etchingstopper film 303 is made of a first organic/inorganic hybrid filmrepresented by SiC_(x)H_(y)O₂ (x>0, y≧0, z≧0) in which the proportion ofthe carbon component is largest.

Subsequently, a lower interlayer insulating film (first interlayerinsulating film) 304 is deposited on the entire surface of the etchingstopper film 303 by plasma CVD, for example. The lower interlayerinsulating film 304 is made of a second organic/inorganic hybrid filmrepresented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z>0) in which the proportionof the carbon component is smallest.

An upper interlayer insulating film (second interlayer insulating film)305 is then deposited on the entire surface of the lower interlayerinsulating film 304 by plasma CVD, for example. The upper interlayerinsulating film 305 is made of a third organic/inorganic hybrid filmrepresented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z>0) in which the proportionof the carbon component is intermediate.

As the film formation gas for deposition of the etching stopper film303, the lower interlayer insulating film 304, and the upper interlayerinsulating film 305, usable is a mixed gas of a material gas such astetramethylsilane (Si(CH₃)₄), dimethyl.dimethylsiloxane(Si(CH₃)₂(—O—CH₃)₂), monomethylsilane (SiH₃ (CH₃)), orHexamethyldisiloxane (Si(CH₃)₃—O—Si(CH₃)₃) and an additive gas such asN₂O. In the fourth embodiment, a mixed gas of hexamethyldisiloxane(HMDSO) and N₂O was used.

The proportion of the carbon component is made smaller in the order ofthe first organic/inorganic hybrid film constituting the etching stopperfilm 303, the third organic/inorganic hybrid film constituting the upperinterlayer insulating film 305, and the second organic/inorganic hybridfilm constituting the lower interlayer insulating film 304, in thefollowing manner, for example. While the same kind of the material gas(for example, HMDSO) is used as the main component, the proportion ofthe additive gas (for example, N₂O) contained in the film formation gasis increased or decreased. Alternatively, a film formation gas includinga material gas containing an increased or decreased amount of the carboncomponent may be selected.

Thereafter, a resist pattern 306 having openings for formation ofcontact holes is formed on the upper interlayer insulating film 305. Theupper and lower interlayer insulating films 305 and 304 are sequentiallyplasma-etched using the resist pattern 306 as a mask.

The same etching gas and etching conditions as those used in the firstembodiment are applied for the plasma etching of the upper and lowerinterlayer insulating films 305 and 304. That is, an etching gas havinga volume flow ratio of:

-   -   C₄F₈:CH₂F₂:Ar:CO:N₂=2:1:10:5:0.5        is fed into the reaction chamber that is kept at a pressure of        2.6 Pa, and plasma of the etching gas is generated to enable        plasma etching.

Under the above conditions, etching proceeds for the upper interlayerinsulating film 305 in the following manner. The etching species such asN₂ contained in the plasma react with carbon atoms or hydrogen atomsexisting on the bottom of the contact hole 307 to reform the bottomduring the etching. Since the upper interlayer insulating film 305contains the carbon component in an intermediate proportion, an etchingreaction gas containing the carbon component is generated in anintermediate amount during the etching of the interlayer insulating film305. This facilitates deposition of a polymer film on the wall and thebottom of the contact hole 307. In addition, the carbon component in theinterlayer insulating film 305 impedes progress of the etching. Theetching rate therefore decreases toward the bottom of the contact hole307. Therefore, the amount of polymer deposited on the wall is greaterthan the amount of progress of the etching toward the bottom. As aresult, as shown in FIG. 11( b), the diameter of the contact hole 307 issmaller toward to the bottom.

Subsequently, in the plasma etching for the lower interlayer insulatingfilm 304, etching proceeds in the following manner. The etching speciessuch as N₂ contained in the plasma react with carbon atoms or hydrogenatoms existing on the bottom of the contact hole 307 to reform thebottom during the etching. The deposition of a polymer film and theetching proceed competing with each other on the bottom of the contacthole 307. However, since the lower interlayer insulating film 304contains the carbon component in the smallest proportion, the carboncomponent contained in an etching reaction gas generated during theetching of the interlayer insulating film 304 is small, and thus theamount of the polymer film deposited on the wall and the bottom of thepolymer film deposited on the wall and the bottom of the contact hole307 is small. Moreover, the carbon component on the surface of theinterlayer insulating film 304 at the bottom of the contact hole 307 hasbeen sufficiently eliminated, and thus the etching rate does notdecrease toward the bottom. Therefore, the etching rate at the bottom ofthe contact hole 307 is large, and the amount of the polymer filmdeposited on the wall is sufficiently small. As a result, as shown inFIG. 11( c), the etching proceeds with the diameter of the contact hole307 being kept constant.

As a result of the above etching process, as shown in FIG. 11( c), thewall of the contact hole 307 expands in a tapered shape near the openingthereof and stands vertical near the bottom thereof. With this shape ofthe contact hole, when a conductive film is deposited on the upperinterlayer insulating film 305 after removal of the resist pattern 306,the contact hole 307 is reliably filled with the conductive film.

In the fourth embodiment, the proportion of the carbon componentcontained in the upper interlayer insulating film 305 is made largerthan that in the lower interlayer insulating film 304. This makes itpossible to reliably form the contact hole 307 having a wall thatexpands in a tapered shape near the opening and stands vertical near thebottom, without the necessity of changing the etching conditions.

In the fourth embodiment, also, by adjusting the thicknesses of theupper interlayer insulating film 305 and the lower interlayer insulatingfilm 304, it is possible to reliably control the heights of the portionof the contact hole 307 having a tapered wall and the portion thereofhaving a vertical wall.

In the fourth embodiment, the proportion of the carbon componentcontained in the lower and upper interlayer insulating films 304 and 305was changed in stages. Alternatively, the proportion of the carboncomponent contained in the organic/inorganic hybrid film may be changedcontinuously.

In the fourth embodiment, the etching stopper film 303 made of the firstorganic/inorganic hybrid film having the largest proportion of thecarbon component was provided under the lower interlayer insulating film304. Alternatively, an etching stopper film made of a silicon nitridefilm, for example, may be provided.

Fifth Embodiment

A semiconductor device and a fabricating method therefor of the fifthembodiment will be described with reference to FIGS. 12( a) to 12(c).

First, as shown in FIG. 12( a), an interconnection layer 402 made of acopper film, an alloy film of copper as a main component, or the like isembedded in an insulating film 401 deposited on a semiconductorsubstrate 400.

An etching stopper film 403 is then deposited on the entire surface ofthe interconnection layer 402 by plasma CVD, for example. The etchingstopper film 403 is made of a first organic/inorganic hybrid filmrepresented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z>0) in which the proportionof the carbon component is relatively large.

Subsequently, an interlayer insulating film 404 is deposited on theentire surface of the etching stopper film 403 by plasma CVD, forexample. The interlayer insulating film 404 is made of a secondorganic/inorganic hybrid film represented by SiC_(x)H_(y)O_(z) (x>0,y≧0, z>0) in which the proportion of the carbon component is relativelysmall.

As the film formation gas for deposition of the etching stopper film 403and the interlayer insulating film 404, usable is a mixed gas of amaterial gas such as tetramethylsilane (Si(CH₃)₄),dimethyl.dimethylsiloxane (Si(CH₃)₂(—O—CH₃)₂), monomethylsilane(SiH₃(CH₃)), or Hexamethyldisiloxane (Si(CH₃)₃—O—Si(CH₃)₃) and anadditive gas such as N₂O. In the fifth embodiment, a mixed gas ofhexamethyldisiloxane (HMDSO) and N₂O was used.

The proportion of the carbon component in the etching stopper film 403can be made larger than that in the interlayer insulating film 404 inthe following manner, for example. The same kind of the material gas(for example, HMDSO) is used as the main component. The proportion ofthe additive gas (for example, N₂O) contained in the film formation gasfor deposition of the etching stopper film 403 is reduced, while theproportion of the additive gas contained in the film formation gas fordeposition of the interlayer insulating film 404 is increased.Alternatively, a film formation gas including a material gas containingan increased amount of the carbon component may be used for depositionof the etching stopper film 403, while a film formation gas including amaterial gas containing a reduced amount of the carbon component may beused for deposition of the interlayer insulating film 404.

Thereafter, a resist pattern 405 having openings for formation ofcontact holes is formed on the interlayer insulating film 404. Theinterlayer insulating film 404 is then plasma-etched using the resistpattern 405 as a mask.

Hereinafter, the plasma etching method will be described in detail.

First, as shown in FIG. 13, first-stage etching is carried out. That is,an etching gas containing fluorine, carbon and nitrogen is fed into thereaction chamber. High-frequency power is applied to the plasmainduction coil, to generate plasma of the etching gas. The plasma isthen attracted to the semiconductor substrate 400.

Under the above conditions, etching proceeds in the following manner.The etching species such as N₂ contained in the plasma react with carbonatoms or hydrogen atoms existing on the bottom of a contact hole 406(see FIG. 12( b)) to reform the bottom during the etching. Since theamount of the N₂ component contained in the etching gas is small, thecarbon component of the interlayer insulating film 404 is lesseliminated at the bottom of the contact hole 406. This impedes progressof the etching toward the bottom, and thus the etching rate toward thebottom of the contact hole 406 decreases. Therefore, the amount of apolymer film deposited on the wall is greater than the amount ofprogress of the etching toward the bottom, and thus, as shown in FIG.12( b), the diameter of the contact hole 407 is smaller toward thebottom.

Subsequently, second-stage etching is carried out as shown in FIG. 13.That is, the added amount of the N₂ gas to the etching gas fed into thereaction chamber is increased so that the proportion of N₂ is as largeas that in the first embodiment (volume flow ratio of N₂ gas/volume flowratio of CF gas is relatively large).

The above etching proceeds while the etching species such as N₂contained in the plasma react with carbon atoms or hydrogen atomsexisting on the bottom of the contact hole 406 thereby reforming thebottom. Since the amount of the N₂ gas contained in the etching gas islarge, the carbon component at the surface of the interlayer insulatingfilm 404 on the bottom of the contact hole 406 has been sufficientlyeliminated. Therefore, the etching rate toward the bottom does notdecrease. In addition, the amount of the polymer film deposited on thewall of the contact hole 406 is sufficiently small. Thus, the etchingproceeds with the diameter of the contact hole 406 being kept constant.

As a result, as shown in FIG. 12( c), formed is the contact hole 406 ofwhich the wall expands in a tapered shape near the opening and standsvertical near the bottom. Therefore, when a conductive film is depositedon the interlayer insulating film 404 after removal of the resistpattern 405, the contact hole 406 is reliably filled with the conductivefilm.

In the fifth embodiment, the amount of the N₂ gas added to the etchinggas is increased during the etching. This makes it possible to reliablyform the contact hole 406 of which the wall expands in a tapered shapenear the opening and stands vertical near the bottom, without changingthe composition of the interlayer insulating film 404.

In the fifth embodiment, the added amount of the N₂ gas was changed instages. Alternatively, the added amount of the N₂ gas may be changecontinuously.

In the fifth embodiment, the etching stopper film 403 made of the firstorganic/inorganic hybrid film in which the proportion of the carboncomponent was relatively large was formed under the interlayerinsulating film 404. Alternatively, an etching stopper film made of asilicon nitride film, for example, may be provided.

Sixth Embodiment

A semiconductor device and a fabricating method therefor of the sixthembodiment will be described with reference to FIGS. 14( a) to 14(c) and15(a) to 15(d).

First, as shown in FIG. 14( a), a lower interconnection 502 made of acopper film, an alloy film of copper as a main component, or the like isembedded in an insulating film 501 deposited on a semiconductorsubstrate 500. An etching stopper film 503 having a thickness of 50 nmis then deposited on the entire surface of the lower interconnection502. The etching stopper film 503 is made of a first organic/inorganichybrid film represented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z≧0) in whichthe proportion of the carbon component is relatively large.

Subsequently, an interlayer insulating film 504 is deposited on theetching stopper film 503 by plasma CVD, for example. The interlayerinsulating film 504 is made of a second organic/inorganic hybrid filmrepresented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z>0) in which the proportionof the carbon component is relatively small.

As the film formation gas for deposition of the etching stopper film 503and the interlayer insulating film 504, usable is a mixed gas of amaterial gas such as tetramethylsilane (Si(CH₃)₄),dimethyl.dimethylsiloxane (Si(CH₃)₂(—O—CH₃)₂), monomethylsilane(SiH₃(CH₃)), or Hexamethyldisiloxane (Si(CH₃)₃—O−Si(CH₃)₃) and anadditive gas such as N₂O.

The proportion of the carbon component in the etching stopper film 503can be made larger than that in the interlayer insulating film 504 inthe following manner, for example. The same kind of the material gas(for example, HMDSO) is used as the main component. The proportion ofthe additive gas (for example N₂O) contained in the film formation gasfor deposition of the etching stopper film 503 is reduced, while theproportion of the additive gas contained in the film formation gas fordeposition of the interlayer insulating film 504 is increased.Alternatively, a film formation gas including a material gas containingan increased amount of the carbon component may be used for depositionof the etching stopper film 503, while a film formation gas including amaterial gas containing a reduced amount of the carbon component may beused for deposition of the interlayer insulating film 504.

Subsequently, a CMP stopper film 505 made of a silicon nitride film, forexample, is deposited on the interlayer insulating film 504. A resistpattern 506 having openings for formation of contact holes is formed onthe CMP stopper film 505. The CMP stopper film 505 is then etched usingthe resist pattern 506 as a mask, so that the openings of the resistpattern 506 are transferred to the CMP stopper film 505.

Referring to FIG. 14( b), the interlayer insulating film 504 isplasma-etched using the resist pattern 506 as a mask.

The conditions of this plasma etching are substantially the same asthose used in the first embodiment. That is, the etching gas containingfluorine, carbon and nitrogen is fed into the reaction chamber, andhigh-frequency power is applied to the plasma induction coil to generateplasma of the etching gas.

Under the above conditions, the etching proceeds in the followingmanner. The etching species such as N₂ contained in the plasma reactwith carbon atoms or hydrogen atoms existing on the bottom of a contacthole 507 to reform the bottom during the etching. That is, the bottom(reformed layer) of the contact hole 507 has a composition close to thatof SiO₂, and therefore is nicely etched with the etching species such asCF_(x) contained in the plasma.

Referring to FIG. 14( c), the resist pattern 506 is removed. Referringto FIG. 15( a), the etching stopper film 503 is etched using the CMPstopper film 505 having openings as a mask. By this etching, the portionof the etching stopper film 503 exposed in the contact hole 507 isremoved. Since the etching stopper film 503 is over-etched, a shallowconcave portion is formed at the surface of the lower interconnection502.

Referring to FIG. 15( b), a metal film 508 made of a copper film, atungsten film, or the like is deposited on the entire surface of the CMPstopper film 505. The portion of the metal film 508 exposed on the CMPstopper film 505 is then removed by CMP, to form a plug 508A made of themetal film 508 as shown in FIG. 15( c). A dishing phenomenon occurs atthe surface of the plug 508A, so that the surface of the plug 508A isrecessed by a depth roughly equal to the thickness of the CMP stopperfilm 505.

Referring to FIG. 15( d), when the CMP stopper film 505 is removed byetching, the surface of the plug 508A is flat and flush with the surfaceof the interlayer insulating film 504. In the case of a multilayerinterconnection structure, the flatness of upper interconnections can beimproved.

If no dishing phenomenon occurs at the surface of the plug 508A, or ifthe thickness of the CMP stopper film 505 is larger than the dishingamount, the surface portion of the plug 508A protrudes from theinterlayer insulating film 504 after the removal of the CMP stopper film505. Such a protrusion may be used as an alignment mark in an alignmentprocess for formation of upper interconnections if the flatness of theresultant upper interconnections is within a permissible range.

In the sixth embodiment, the contact hole 507 can be reliably formedthrough the interlayer insulating film 504 made of the organic/inorganichybrid film having a low specific dielectric constant. In addition, CMPcan be performed nicely for the interlayer insulating film 504 made ofan organic/inorganic hybrid film considered poor in CMP resistancebecause the interlayer insulating film 504 is protected with the CMPstopper film 505 during the CMP process.

Moreover, the etching stopper film 503 made of the organic/inorganichybrid film having a larger proportion of the carbon component is formedunder the interlayer insulating film 504. This etching stopper film 503,which serves as the etching stopper for the interlayer insulating film504, is significantly small in specific dielectric constant comparedwith the conventional etching stopper film made of a silicon nitridefilm.

Seventh Embodiment

A semiconductor device and a fabricating method therefor of the seventhembodiment of the present invention will be described with reference toFIGS. 16( a) to 16(c), 17(a) to 17(c), and 18(a) to 18(d).

First, as shown in FIG. 16( a), a lower interconnection 602 made of acopper film, an alloy film of copper as a main component, or the like isembedded in an insulating film 601 deposited on a semiconductorsubstrate 600. An etching stopper film 603 having a thickness of 50 nmis then deposited on the entire surface of the lower interconnection.602. The etching stopper film 603 is made of a first organic/inorganichybrid film represented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z>0) in whichthe proportion of the carbon component is relatively large.

Subsequently, an interlayer insulating film 604 is deposited on theetching stopper film 603 by plasma CVD, for example. The interlayerinsulating film 604 is made of a second organic/inorganic hybrid filmrepresented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z>0) in which the proportionof the carbon component is relatively small.

As the film formation gas for deposition of the etching stopper film 603and the interlayer insulating film 604, usable is a mixed gas of amaterial gas such as tetramethylsilane (Si(CH₃)₄),dimethyl.dimethylsiloxane (Si(CH₃)₂(—O—CH₃)₂), monomethylsilane(SiH₃(CH₃)), or Hexamethyldisiloxane (Si(CH₃)₃—O—Si(CH₃)₃) and anadditive gas such as N₂O.

The proportion of the carbon component in the etching stopper film 603can be made larger than that in the interlayer insulating film 604 inthe following manner, for example. The same kind of the material gas(for example, HMDSO) is used as the main component. The proportion ofthe additive gas (for example N₂O) contained in the film formation gasfor deposition of the etching stopper film 603 is reduced, while theproportion of the additive gas contained in the film formation gas fordeposition of the interlayer insulating film 604 is increased.Alternatively, a film formation gas including a material gas containingan increased amount of the carbon component may be used for depositionof the etching stopper film 603, while a film formation gas including amaterial gas containing a reduced amount of the carbon component may beused for deposition of the interlayer insulating film 604.

Subsequently, a CMP stopper film 605 made of a silicon nitride film, forexample, is deposited on the interlayer insulating film 604. A firstresist pattern 606 having for formation of contact holes is formed onthe CMP stopper film 605. The CMP stopper film 605 is then etched usingthe first resist pattern 606 as a mask, so that the openings of thefirst resist pattern 606 are transferred to the CMP stopper film 605.

Referring to FIG. 16( b), the interlayer insulating film 604 isplasma-etched using the first resist pattern 606 as a mask.

The conditions of this plasma etching are substantially the same asthose used in the first embodiment. That is, the etching gas containingfluorine, carbon and nitrogen is fed into the reaction chamber, andhigh-frequency power is applied to the plasma induction coil to generateplasma of the etching gas.

Under the above conditions, the etching proceeds in the followingmanner. The etching species such as N₂ contained in the plasma reactwith carbon atoms or hydrogen atoms existing on the bottom of a contacthole 607 to reform the bottom during the etching. That is, the bottom(reformed layer) of the contact hole 607 has a composition close to thatof SiO₂, and therefore is nicely etched with the etching species such asCF_(x) contained in the plasma.

After the first resist pattern 606 is removed as shown in FIG. 16( c), asecond resist pattern 608 having openings for formation ofinterconnection grooves is formed on the CMP stopper film 605 as shownin FIG. 17( a).

Using the second resist pattern 608 as a mask, the CMP stopper film 605and then the interlayer insulating film 604 are sequentially etched, toform an interconnection groove 609 communicating with the contact hole607 in the interlayer insulating film 604 as shown in FIG. 17( b). Theconditions for the etching for formation of the interconnection groove609 in the interlayer insulating film 604 are the same as those forformation of the contact hole 607 through the interlayer insulating film604.

After the second resist pattern 608 is removed as shown in FIG. 17( c),the portion of the etching stopper film 603 exposed in the contact hole607 is removed as shown in FIG. 18( a).

Referring to FIG. 18( b), a metal film 610 made of a copper film, atungsten film, or the like is deposited on the entire surface of the CMPstopper film 605. The portion of the metal film 610 exposed on the CMPstopper film 605 is then removed by CMP, to form a plug 610A and anupper interconnection 610B made of the metal film 610 simultaneously asshown in FIG. 18( c).

Referring to FIG. 18( d), when the CMP stopper film 605 is removed byetching, the surface of the upper interconnection 610B is flat and flushwith the surface of the interlayer insulating film 604.

In the seventh embodiment, the contact hole 607 and the interconnectiongroove 609 can be reliably formed in the interlayer insulating film 604made of an organic/inorganic hybrid film having a low specificdielectric constant. In addition, CMP can be performed nicely for theinterlayer insulating film 604 made of an organic/inorganic hybrid filmconsidered poor in CMP resistance, because the interlayer insulatingfilm 604 is protected with the CMP stopper film 605 during the CMPprocess.

Moreover, the etching stopper film 603 made of the organic/inorganichybrid film having a larger proportion of the carbon component is formedunder the interlayer insulating film 604. This etching stopper film 603,which serves as the etching stopper for the interlayer insulating film604, is significantly small in specific dielectric constant comparedwith the conventional etching stopper film made of a silicon nitridefilm.

Eighth Embodiment

A semiconductor device and a fabricating method therefor of the eighthembodiment will be described with references to FIGS. 19( a) to 19(c)and 20(a) to 20(c).

First, a lower interconnection 702 made of a copper film, an alloy filmof copper as a main component, or the like is embedded in an insulatingfilm 701 deposited on a semiconductor substrate 700. An etching stopperfilm 703 having a thickness of 50 nm is then deposited on the entiresurface of the lower interconnection 702. The etching stopper film 703is made of an insulating film represented by SiC_(x)H_(y)O_(z) (x>0,y≧0, z>0) in which the proportion of the carbon component is relativelylarge.

Subsequently, an interlayer insulating film 704 is deposited on theetching stopper film 703 by plasma CVD, for example. The interlayerinsulating film 704 is made of an organic/inorganic hybrid filmrepresented by SiC_(x)H_(y)O_(z) (x>0, y≧0, z>0) in which the proportionof the carbon component is relatively small.

As the film formation gas for deposition of the etching stopper film 703and the interlayer insulating film 704, usable is a mixed gas of amaterial gas such as tetramethylsilane (Si(CH₃)₄),dimethyl.dimethylsiloxane (Si(CH₃)₂(—O—CH₃)₂), monomethylsilane(SiH₃(CH₃)), or Hexamethyldisiloxane (Si(CH₃)₃—O—Si(CH₃)₃) and anadditive gas such as N₂O.

The proportion of the carbon component in the etching stopper film 703can be made larger than that in the interlayer insulating film 704 inthe following manner, for example. The same kind of the material gas(for example, HMDSO) is used as the main component. The proportion ofthe additive gas (for example N₂O) contained in the film formation gasfor deposition of the etching stopper film 703 is reduced, while theproportion of the additive gas contained in the film formation gas fordeposition of the interlayer insulating film 704 is increased.Alternatively, a film formation gas including a material gas containingan increased amount of the carbon component may be used for depositionof the etching stopper film 703, while a film formation gas including amaterial gas containing a reduced amount of the carbon component may beused for deposition of the interlayer insulating film 704.

Thereafter, a silicon oxide film 705 containing no carbon component,such as a TEOS film, having a thickness of 5 nm to 10 nm is deposited onthe interlayer insulating film 704 by plasma CVD, for example. Apositive chemical amplification resist material is then applied to thesilicon oxide film 705, to form a resist film 706.

The resist film 706 is then patterned by being exposed to light via amask 707. By this pattern exposure, an exposed portion 706 a of theresist film 706 is made soluble to a developer by the function of acidgenerated from an acid generator, while non-exposed portions 706 b ofthe resist film 706 remain hard to dissolve in the developer withoutgeneration of acid from an acid generator. During this process, with theexistence of the silicon oxide film 705 containing no carbon componentinterposed between the resist film 706 and the interlayer insulatingfilm 704, acid (H⁺) generated in the exposed portion 706 a of the resistfilm 706 is prevented from reacting with a carbon component (C)contained in the interlayer insulating film 704, and thus is notdeactivated. It is therefore ensured that the exposed portion 706 a ismade soluble to the developer by the function of acid.

Thereafter, as shown in FIG. 19( b), the exposed portion 706 a of theresist film 706 is removed by being dissolved in the developer, to forma first resist pattern 708 that is composed of the non-exposed portions706 b of the resist film 706 and has openings for formation of contactholes. Since the exposed portion 706 a of the resist film 706 has beenmade soluble to the developer without deactivation of acid as describedabove, the resultant first resist pattern 708 is excellent inresolution.

Referring to FIG. 19( c), the opening of the first resist pattern 708 istransferred to the silicon oxide film 705, and then the interlayerinsulating film 704 is plasma-etched using the first resist pattern 708as a mask, to form a contact hole 709 through the interlayer insulatingfilm 704.

The conditions of this plasma etching are substantially the same asthose used in the first embodiment. That is, the etching gas containingfluorine, carbon and nitrogen is fed into the reaction chamber, andhigh-frequency power is applied to the plasma induction coil to generateplasma of the etching gas.

Under the above conditions, the etching proceeds in the followingmanner. The etching species such as N₂ contained in the plasma reactwith carbon atoms or hydrogen atoms existing on the bottom of a contacthole 709 to reform the bottom during the etching. Therefore, the bottomof the contact hole 709 is nicely etched with the etching species suchas CF_(x) contained in the plasma.

Referring to FIG. 20( a), before or after removal of the resist pattern708 with oxygen plasma, the wall of the contact hole 709 is exposed to anitrogen-containing gas or a gas containing fluoride, carbon andnitrogen, to form a reformed layer 710 on the wall of the contact hole709 by eliminating the carbon component from the organic/inorganichybrid film.

Referring to FIG. 20( b), after the removal of the first resist pattern708, a second resist pattern 711 made of a chemical amplification resistmaterial having openings for formation of interconnection grooves isformed on the silicon oxide film 705. With the existence of the siliconoxide film 705 having no carbon component interposed between thechemical amplification resist film and the interlayer insulating film704, and the formation of the reformed layer 710 containing no carboncomponent on the wall of the contact hole 709, acid generated in anexposed portion of the resist film is prevented from being deactivated.Thus, the resultant second resist pattern 711 is excellent inresolution.

Referring to FIG. 20( c), the opening of the second resist pattern 711is transferred to the silicon oxide film 705, and then the interlayerinsulating film 704 is plasma-etched using the second resist pattern 711as a mask, to form an interconnection groove 712 in the interlayerinsulating film 704.

The conditions for the above etching are the same as those used in thefirst embodiment. That is, the etching gas containing fluorine, carbonand nitrogen is fed into the reaction chamber, and high-frequency poweris applied to the plasma induction coil to generate plasma of theetching gas.

Under the above conditions, the etching proceeds in the followingmanner. The etching species such as N₂ contained in the plasma reactwith carbon atoms or hydrogen atoms existing on the bottom of theinterconnection groove 712 to reform the bottom during the etching.Therefore, the bottom of the interconnection groove 712 is nicely etchedwith the etching species such as CF_(x) contained in the plasma.

Thereafter, although illustration is omitted, the following processesare carried out as in the seventh embodiment. After removal of thesecond resist pattern 711, the portion of the etching stopper film 703exposed in the contact hole 709 is removed. Before or after the removalof the resist pattern 711, the reformed layer 710 may be removed byoxide film etching. Thereafter, a metal film made of a copper film or atungsten film is deposited on the entire surface of the silicon oxidefilm 705. The portion of the metal film exposed on the silicon oxidefilm 705 is then removed by CMP, to obtain multilayer interconnectionshaving a dual damascene structure.

In the eighth embodiment, the resist film 706 made of a positivechemical amplification resist material was used. When a resist film madeof a negative chemical amplification resist material is used, also,deactivation of acid in the exposed portion of the resist film can beprevented by interposing the silicon oxide film 705 containing no carboncomponent between the interlayer insulating film 704 and the negativeresist film.

In the case that a reflection prevention film is provided by CVD at aposition lower than the resist film 706 shown in FIG. 19( a), it ispreferable to form the reflection prevention film on the interlayerinsulating film 704 and then the silicon oxide film 705 on thereflection prevention film. By this structure, it is possible to preventdeactivation of acid in the resist film 706 caused due to the existenceof the reflection prevention film based on a mechanism, different fromthat in the case of the organic/inorganic hybrid film, that works whenthe underlying layer is an alkaline film or a film other than theorganic/inorganic hybrid film that easily binds with H⁺.

(First Modification of the Eighth Embodiment)

In the eighth embodiment, the silicon oxide film 705 containing nocarbon component was deposited on the interlayer insulating film 704made of the organic/inorganic hybrid film. In the first modification ofthe eighth embodiment, the silicon oxide film 705 containing no carboncomponent is formed on the interlayer insulating film 704 by reformingthe surface portion of the interlayer insulating film 704 made of theorganic/inorganic hybrid film.

First, as in the eighth embodiment, the interlayer insulating film 704made of the organic/inorganic hybrid film is deposited.

The interlayer insulating film 704 is then etched back with an etchinggas containing fluorine and carbon. At the final stage of this etch-backprocess, an etching gas containing fluorine, carbon and nitrogen is fedand plasma is generated from the etching gas. The etching species suchas N₂ contained in the plasma are attracted to the surface portion ofthe interlayer insulating film 704 and react with carbon atoms orhydrogen atoms existing on the surface portion. Thus, the surfaceportion of the interlayer insulating film 704 is reformed by theelimination of the carbon component, forming the silicon oxide film 705.

Thereafter, a chemical amplification resist material is applied to thesilicon oxide film 705 formed on the interlayer insulating film 704, toform the resist film 706, as in the eighth embodiment. The resist film706 is then subjected to pattern exposure, and the exposed portion 706 aof the resist film 706 is removed with a developer, to form the firstresist pattern 708.

By the above method, the silicon oxide film 705 containing no carboncomponent exists between the resist film 706 and the interlayerinsulating film 704. Therefore, as in the eighth embodiment,deactivation of acid generated in the exposed portion 706 a of theresist film 706 is prevented. It is therefore ensured that the exposedportion 706 a is made soluble to the developer by the function of acid.

(Second Modification of the Eighth Embodiment)

A semiconductor device and a fabricating method therefor of the secondmodification of the eighth embodiment will be described with referenceto FIGS. 21( a) to 21(c).

First, as in the eighth embodiment, the interlayer insulating film 704is plasma-etched using the first resist pattern 708 as a mask, to formthe contact hole 709 through the interlayer insulating film 704 (seeFIG. 19( c)). The reformed layer 710 is then formed as shown in FIG. 20(a). Thereafter, the first resist pattern 708 is removed by ashing withoxygen plasma.

Thereafter, a chemical amplification resist material is applied to thesilicon oxide film 705, to form a resist film. The resist film is thensubjected to pattern exposure and development, to form the second resistpattern 711 having openings for formation of interconnection grooves asshown in FIG. 21( a). During this process, the chemical amplificationresist material is also deposited in the contact hole 709. In the resistfilm deposited in the contact hole 709, acid generated due to thepattern exposure is deactivated by the carbon component from the etchingstopper film 703. Therefore, the resist film on the bottom of thecontact hole 709 is left behind after the removal of the exposed portionof the resist film with the developer, forming a protection film 711 amade of the chemical amplification resist material in which acid hasbeen deactivated.

The opening of the second resist pattern 711 is transferred to thesilicon oxide film 705, and then the interlayer insulating film 704 isplasma-etched using the second resist pattern 711 as a mask to form aninterconnection groove 712 in the interlayer insulating film 704 asshown in FIG. 21( b).

The conditions for the above etching are the same as those used in thefirst embodiment. That is, the etching gas containing fluorine, carbonand nitrogen is fed into the reaction chamber, and high-frequency poweris applied to the plasma induction coil to generate plasma of theetching gas. Under the above conditions, the etching proceeds in thefollowing manner. The etching species such as N₂ contained in the plasmareact with carbon atoms or hydrogen atoms existing on the bottom of theinterconnection groove 712 to reform the bottom during the etching.Therefore, the bottom of the interconnection groove 712 is nicely etchedwith the etching species such as CF_(x) contained in the plasma.

The interlayer insulating film 704 is subjected to two times of plasmaetching, one for formation of the contact hole 709 and the other forformation of the interconnection groove 712. Therefore, the portion ofthe etching stopper film 703 exposed in the contact hole 709 maypossibly be extremely thinned or even completely lost (see FIG. 20( c)).Therefore, during the ashing of the second resist pattern 711 withoxygen plasma, the lower interconnection 702 may be exposed to theoxygen plasma forming a naturally oxidized film on the surface of thelower interconnection 702. This may increase the contact resistancebetween the plug made of a conductive film filled in the contact hole709 and the lower interconnection 702.

In the second modification of the eighth embodiment, the plasma etchingfor formation of the interconnection groove 712 is carried out with theprotection film 711 a made of the acid-deactivated chemicalamplification resist material existing on the bottom of the contact hole709. The etching stopper film 703 is therefore exposed to plasma etchingonly once, and thus the portion of the etching stopper film 703 exposedin the contact hole 709 is prevented from being excessively thinned.

For the above reason, as shown in FIG. 21( c), when the second resistpattern 711 is removed by ashing with oxygen plasma, the lowerinterconnection 702 is prevented from being exposed to the oxygenplasma. This prevents formation of a naturally oxidized film on thesurface of the lower interconnection 702, and thus prevents increase inthe contact resistance between the plug made of a conductive film filledin the contact hole 709 and the lower interconnection 702.

Moreover, since the etching stopper film 703 is exposed to plasmaetching only once, the etching stopper film 703 having a small thicknesscan be used. Thus, a material that deactivates a resist, such as anorganic/inorganic hybrid film, can be used as the etching stopper film703. Since the thickness of the etching stopper film 703 can be small,also, the specific dielectric constant between the lower and upperinterconnections can be reduced. In addition, the thickness of theinterlayer insulating film can be reduced, and thus the variation inthickness can be minimized.

1. An etching method for plasma-etching an organic/inorganic hybrid filmhaving low dielectric constant and represented by SiC_(x)H_(y)O_(z)(x>0, y>0, z>0), comprising: a first step of plasma-etching theorganic/inorganic hybrid film with an etching gas containing fluorine,carbon and nitrogen, a second step of plasma-etching theorganic/inorganic hybrid film with a nitrogen free etching gascontaining fluorine and carbon after the first step, wherein the carboncontent in the organic/inorganic hybrid film is about more than 17% andno more than 37%.
 2. The etching method of claim 1, wherein the etchinggas contains CO or CO₂.
 3. The etching method of claim 1, wherein theplasma-etching step includes a sub-step of forming an opening in theorganic/inorganic hybrid film by performing plasma etching using aresist pattern as a mask.
 4. The etching method of claim 1, whereinduring the plasma-etching step, C_(x)H_(y) is changed into HCN or CN atthe surface of the organic/inorganic hybrid film.
 5. The etching methodof claim 1, wherein the organic/inorganic hybrid film includes a methylgroup.
 6. A fabricating method for a semiconductor device, comprisingthe steps of: depositing an interlayer insulating film on aninterconnection layer formed on a substrate, the interlayer insulatingfilm being composed of an organic/inorganic hybrid film having lowdielectric constant and represented by SiC_(x)H_(y)O_(z) (x>0, y>0,z>0); forming a resist pattern having an opening on the interlayerinsulating film, performing a first plasma etching on theorganic/inorganic film with an etching gas containing fluorine, carbonand nitrogen and using the resist pattern as a mask, thereby forming acontact hole or an interconnection groove in the interlayer insulatingfilm; and performing a second plasma etching on the organic/inorganichybrid film with a nitrogen free etching gas containing fluorine andcarbon after the first plasma etching, wherein the carbon content in theorganic/inorganic hybrid film is about more than 17% and no more than37%.
 7. The fabricating method for a semiconductor device of claim 6,wherein during the plasma-etching step, C_(x)H_(y) is changed into HCNor CN at the surface of the organic/inorganic hybrid film.
 8. Thefabricating method for a semiconductor device of claim 6, wherein theorganic/inorganic hybrid film includes a methyl group.
 9. A fabricatingmethod for a semiconductor device, comprising the steps of: depositingan interlayer insulating film on an interconnection layer formed on asubstrate, the interlayer insulating film being composed of anorganic/inorganic hybrid film having low dielectric constant andrepresented by SiC_(x)H_(y)O_(z) (x>0, y>0, z>0); forming a resistpattern having an opening on the interlayer insulating film; performinga plasma etching on the interlayer insulating film with an etching gascontaining fluorine, carbon and nitrogen and using the resist pattern asa mask, thereby forming a contact hole or an interconnection groove inthe interlayer insulating film; and performing a second plasma etchingon the interlayer insulating film with a nitrogen free etching gascontaining fluorine and carbon after the first plasma etching, whereinthe carbon content in the organic/inorganic hybrid film is about morethan 17% and no more than 37%.
 10. The fabricating method for asemiconductor device of claim 9, wherein C_(x)H_(y) is changed into HCNor CN at the surface of the organic/inorganic hybrid film.
 11. Thefabricating method for a semiconductor device of claim 9, wherein theorganic/inorganic hybrid film includes a methyl group.
 12. An etchingmethod for plasma-etching an organic/inorganic hybrid film representedby SiC_(x)H_(y)O_(z) (x>0, y>0, z>0), comprising: a first step ofplasma-etching the film with an etching gas containing fluorine, carbonand nitrogen, and a second step of plasma-etching the film with anitrogen free etching gas containing fluorine and carbon after the firststep.